PhD Research Topics

Topics available for the research phase of the program

If you apply directly for the research phase since you already obtain a qualifying master's degree, you will have to state your preferences for at least one and a maximum of three of our research fields. The Fellows working in the respective research field(s) will then review your application and you might already meet them in the application interviews.

On this page, you find a list of all our research fields. With a click on each field, you find sample PhD topics of the individual Fellows that are currently available. Please note that the topics might change until you start your research phase at the MPSP, or the Fellows might also provide you with individual topics. Nevertheless, the listed Ph.D. topics should serve as initial inspiration and decision-making aid for your preferred research fields.

If you want to learn more about the individual Fellows, you can check them out here


Prof. Henry Chapman (Hamburg)
  • Lensless Imaging using Coherent Electrons
  • The methods of coherent diffractive imaging and ptychography replace a lens with an algorithm to obtain quantitative phase-sensitive images, and may provide advantages over conventional electron microscopy of macromolecules. This project will develop simulations of coherent electron diffraction under realistic conditions and compare with experiments, and investigate new algorithms to recover images from the diffraction data. We are looking for a candidate with a strong interest in imaging and Fourier optics, and who is capable of programming and performing data visualisation.

  • High resolution X-ray holography
  • One aspect of in-line holography is that the reference wave greatly amplifies the weak scattered wave from a small object such as a virus. With revolutionary new X-ray optics it becomes possible to record highly magnified in-line holograms of nanometer-sized objects. This project will explore the potentials of this for imaging biological materials, investigate the dose requirements, and experimentally demonstrate 3D imaging. The successful candidate should have a strong background in optics and imaging, and strong programming skills.

  • Time-resolved serial crystallography
  • This project will extend the method of serial femtosecond crystallography using X-ray free-electron lasers and synchrotron radiation facilities to investigate the dynamics of proteins induced by novel triggers, such as terahertz radiation or photo-acoustic waves. The candidate will have a unique opportunity to work on forefront research at advanced X-ray facilities as well as develop and test new experimental methods in the laboratory. The project combines experimental physics, structural biology, and computational analysis. We are therefore searching for a candidate with a strong interest in multidisciplinary research.


    Dr. Maria Chekhova (Erlangen-Nürnberg)
  • Third-order parametric down-conversion
  • The goal is to experimentally observe a new nonlinear optical effect: direct decay of a photon in three, the inverse to the third harmonic generation. This effect, called third-order parametric down-conversion, is an upgrade of spontaneous parametric down-conversion (SPDC). It is far more unusual and interesting than SPDC: it results in quantum states of light with negative Wigner functions and it offers a realization of a cubic quantum gate, highly demanded in quantum information. Despite many theoretical works and several experimental attempts with nonlinear crystals, waveguides, and fibers, it has been not observed so far. In this PhD project the concept is to use a new class of materials, namely ultrathin layers with giant cubic nonlinearities (semiconductors, chalcogenide glass, metasurfaces) where phase matching will be not needed.

  • Loss-tolerant quantum imaging with twin beams
  • One of the ways to enhance signal-to-noise ratio in imaging is to illuminate an object with twin beams, for which the photon numbers are correlated. Such twin beams are produced at the output of a nonlinear crystal through high-gain parametric down-conversion. However, this technique is useless if the detection efficiency is not extremely high. The project aims at further developing this technique by adding phase sensitive parametric amplification of the image, which will make the imaging tolerant to any loss and therefore suitable for ‘difficult’ spectral ranges like IR and terahertz.


    Prof. Stefan Hell (Göttingen)
  • Far-Field Optical Imaging at Molecular Resolution
  • New concepts have radically overcome the longstanding limits to optical analysis of molecular systems. Optical resolutions of a few nano¬meters have been demonstrated, well beyond Abbe’s diffraction limit, for example with the recent MINFLUX concept (Science 355, 606-612 (2017)). This opens up entirely new experimental opportunities, breaking new ground in the study of macromolecules and beyond. The successful candidate will develop advanced optical instrumentation and investigate physical imaging conditions and resolution performance. Alternatively, a related project involving theoretical optical analysis and modelling can be offered. The candidate should have (or expect to complete soon) a Master’s or equivalent degree in Physics or Physical Chemistry or a comparable qualification.


    Prof. Ulrich Nienhaus (Karlsruhe)
  • Advanced Flourescence Microscopy
  • Stimulated emission depletion (STED) nanoscopy is a super-resolution fluorescence imaging technique to study biomolecular interactions in living systems at the highest possible temporal and spatial resolution. In this research, STED nanoscopy-based instrumentation will be advanced through implementation of ultrafast laser beam scanners and adaptive optics for suppression of aberrations. Moreover, novel data analysis tools based on single particle tracking and spatial/temporal correlations of pixel intensities will be developed and used for a range of biophysical experiments on living systems (cells, tissues organisms).


    Prof. Gerhard Paulus (Jena)
  • Strong-field laser physics
  • A central goal of molecular physics is to steer the outcome of chemical reactions. Ultrashort laser pulses provide a powerful tool to study and also control molecular bonds on ultrashort time scales. However, the interaction of molecules with laser pulses is governed by the excitation of bound or unbound electronic states, while most conventional chemistry proceeds on the electronic ground state via excitation of vibrational levels. Using ultrashort IR lasers, we strive to investigate the largely unexplored field of ground-state photochemistry. To this end, we use highly sophisticated laser technology as well as an advanced ion beam apparatus with time- and position-resolved coincidence detection. Available topics range from instrumentation and laser technology to data analysis and theoretical simulations.

  • Nanoscale XUV imaging
  • XUV radiation has distinctive advantages for imaging, including resolution and element-specific contrast. We recently invented XUV coherence tomography (XCT), which enables non-destructive cross-sectional imaging with nanoscale resolution. Available topics include the combination with other lens-less imaging modalities, ultrafast nanoscale imaging, and multispectral imaging.

  • Precision X-ray polarimetry
  • We have developed X-ray polarimeters providing extinction ratios of better than 1E-10, by far the best in the world and also by far beyond of what is possible in the optical regime. The ultimate goal is to measure the birefringence of vacuum polarized by a strong laser – and we believe that we have sufficiently advanced X-ray polarimetry to do such an experiment at the European XFEL in the next years. However, precision X-ray polarimetry offers a large range of other research opportunities. One of these is X-ray polarization microscopy. Another, in collaboration with Professor Röhlsberger, X-ray quantum optics.

  • Making molecular movies using coincidence spectroscopy
  • The ultimate goal of ultrafast molecular science is to make a movie that allows one to directly watch the motion of nuclei and electrons inside a molecule. Such a movie would provide microscopic insights into light-induced dynamics and chemical reactions that have thus far been inaccessible. Femtosecond laser pulses allow one to access the natural time scale of molecular dynamics. In this project, the potential film director will use a high-power, high-repetition rate femtosecond laser and combine it with a newly acquired coincidence imaging apparatus to record movies of electronic structure changes in molecules as they undergo dynamics.


    Prof. Thomas Pertsch (Jena)
  • Nanoscale photon control for next generation ultrafast integrated quantum systems
  • Nanoscale photon control for next generation ultrafast integrated quantum systems: We are looking for talented candidates, who are sharing the enthusiasm for nanoscale quantum photonics with us. This research field, with its multiple challenges in fundamental physics, quantitative modelling of complex multiphysics problems, nanotechnology, and experimental physics, is an ideal area for qualification of young scientists seeking career opportunities at the forefront of science & research. A PhD project in this field would involve the design, technological realization, and experimental characterization of nonlinear photonic nanostructures for photonic quantum state generation and detection. Besides curiosity-driven fundamental research in nanophotonics, the work would incorporate connections to application-driven projects for quantum imaging and sensing.


    Prof. Jürgen Popp (Jena)
  • Coherent biomedical Raman Imaging by means of ultrafast tunable laser sources
  • Novel Laser based techniques for imaging and spectroscopy, e.g., optical coherence tomography or coherent Raman imaging, are highly promising for biomedical applications. While techniques like stimulated Raman scattering put highest demands on the laser specifications, e.g., in terms of tuning range, tuning speed, bandwidth or noise, for successful clinical translation the laser systems have to be at the same time robust, compact and easy to use. In the group of Prof. Limpert custom-designed ultrafast fiber lasers are developed. Therefore, the aim of this work is to explore, adapt and apply novel laser concepts from the research group of Prof. Limpert (e.g., Fourier-domain mode locked lasers, four wave mixing frequency conversion) in biomedical imaging and spectroscopy, like hyperspectral coherent Raman imaging in the vibrational fingerprint region or multiplex coherent imaging of Raman tags. Furthermore, novel CARS excitation schemes for super resolution vibrational imaging beyond the Abbe limit utilizing the aforementioned laser sources should be explored.


    Prof. Nina Rohringer (Hamburg)
  • X-ray diffraction from population-inverted atoms: opportunities for single-particle imaging
  • X-rays provide a unique opportunity to obtain the structure of matter at atomic resolution. In crystals (periodic arrangement of atomic or molecular constituents) x-ray diffraction is successfully used over more than 100 years to unravel the atomic and electronic structure with applications ranging from simple materials to large biological complexes. Despite the advent of novel, ultrabright x-ray sources -- x-ray free-electron lasers (XFELs) -- the study of single particles of biological interest remains challenging. The challenge manifests itself in the inherently small elastic x-ray scattering strength (giving rise to diffraction) combined with strong competing processes such as ionization and/or Compton scattering. In this project, we will develop a novel imaging technique, relying on two-color pulses of XFELs: The first x-ray pulse will prepare atoms of the sample in core-excited states by promoting an electron of the inner-most electronic shell into a valence shell. The second x-ray pulse, tuned to an inner-shell transition (for example K- transition), will elastically scatter on a set of atoms in states of population inversion. Two effects will enhance the scattering signal: On resonance, anomalous x-ray scattering gives an enhancement of the scattering strength. Moreover, scattering on core-inverted atoms can result in stimulated emission, that eventually gives rise to an exponentially enhanced signal amplification. The signal from population-inverted atoms can be analyzed together with non-resonant scattering from other atoms of the object, thus enhancing the contrast. The successful candidate will develop the concept and theory of the novel approach and in the later stage of the project, will participate in proof-of-concept experiments at XFEL sources.


    Prof. Claus Ropers (Göttingen)
  • Development of Ultrafast Low-Energy Electron Microscopy
  • In this Project, a new concept for real-space imaging of ultrafast dynamics at surfaces is to be developed. We plan to integrate a pulsed photoemission electron source with a low-energy electron microscope. This will allow for the surface-sensitive mapping of ultrafast structural phase transitions, and the generation and propagation of collective excitations.


    Prof. Henry Chapman (Hamburg)
  • Lensless Imaging using Coherent Electrons
  • The methods of coherent diffractive imaging and ptychography replace a lens with an algorithm to obtain quantitative phase-sensitive images, and may provide advantages over conventional electron microscopy of macromolecules. This project will develop simulations of coherent electron diffraction under realistic conditions and compare with experiments, and investigate new algorithms to recover images from the diffraction data. We are looking for a candidate with a strong interest in imaging and Fourier optics, and who is capable of programming and performing data visualisation.

  • High resolution X-ray holography
  • One aspect of in-line holography is that the reference wave greatly amplifies the weak scattered wave from a small object such as a virus. With revolutionary new X-ray optics it becomes possible to record highly magnified in-line holograms of nanometer-sized objects. This project will explore the potentials of this for imaging biological materials, investigate the dose requirements, and experimentally demonstrate 3D imaging. The successful candidate should have a strong background in optics and imaging, and strong programming skills.

  • Time-resolved serial crystallography
  • This project will extend the method of serial femtosecond crystallography using X-ray free-electron lasers and synchrotron radiation facilities to investigate the dynamics of proteins induced by novel triggers, such as terahertz radiation or photo-acoustic waves. The candidate will have a unique opportunity to work on forefront research at advanced X-ray facilities as well as develop and test new experimental methods in the laboratory. The project combines experimental physics, structural biology, and computational analysis. We are therefore searching for a candidate with a strong interest in multidisciplinary research.


    Prof. Peter Hommelhoff (Erlangen)
  • Ultrafast coherent electron dynamics in solids: towards petahertz electronics
  • With phase-controlled laser fields, we have driven electrons inside of graphene fully coherently. We have demonstrated Landau-Zener-Stückelberg interferometry, so subsequent coherent Landau-Zener transitions, leading to a net current (Nature 2017). Based on this, we have further demonstrated more complex coherent current control driven on optical time scales. These insights allow us to now move towards electronics on optical timescales, i.e., petahertz electronics. Both the fundamental physics in various materials and at heterostructures as well as initial building blocks are on our research agenda.


    Prof. Franz Kärtner (Hamburg)
  • Strong-field Physics / Attosecond Science
  • We us sub-cycle parametric waveform synthesis to generate and control isolated attosecond pulses in the EUV to soft-x-ray region for attosecond transient absorption spectroscopy and apply this technique to various fundamental processes such as radiolysis in water, chemical processes in energy conversion and controlled attosecond electron wave packet generation.


  • THz-Enabled Ultrafast Electron Diffraction (UED)
  • Strong THz fields enable ultrabright und ultrashort electron bunches for UED. Here we develop novel THz driven electron guns, accelerators and beam manipulation devices to enhance UED. The basis can be a regular DC- or RF-gun followed by a THz pulse compressor or a combination of THz accelerator and bunch compressor to enable relativistic electron beams from compact devices. The developed UED setups are used in various collaborations to study biochemical processes and quantum materials.


    Prof. Matthias Kling (Munich)
  • Attosecond imaging and spectroscopy of light-induced dynamics in molecules and nanostructures
  • We are interested in ultrafast correlated and collective electron dynamics that unfold when complex materials are exposed to intense, ultrashort laser fields. In particular this includes the attosecond control and tracing of strongly coupled electron-nuclear dynamics in quantum systems such as molecules, and of collective electron dynamics in nanostructured materials, and lightwave-driven petahertz (nano)electronics. We develop and use multi-dimensional imaging techniques in conjunction with (attosecond) pump-probe experiments to gain detailed insight into the dynamics from the interaction of these materials with near-single cycle laser fields of typically attosecond to femtosecond duration. We actively push the theoretical modeling of the rather complex multi-charge dynamics, which are partly carried out in our group using Monte-Carlo simulations with more intricate models within collaborations.


    Prof. Peter Loosen (Aachen)
  • Advanced optical systems for materials processing with high-power ultrashort pulse lasers
  • As the performance of ultrashort pulse lasers increases, so do the challenges for the optical systems to make the provided power available to the process. The increasing power enables the parallelization of processes by using multibeam optics. For beam splitting, diffractive optical elements (DOE) are often used which have to be designed according to the application. At the same time, there is a demand to be able to manipulate each partial beam individually. The design is especially challenging for systems with a high number (> 50) of partial beams. Due to the use of increasingly shorter pulses, the compensation of chromatic effects also becomes important, which increases the complexity of the optical systems. The consideration of the mentioned effects as well as the fulfillment of the requirements for photonic production processes require a multidisciplinary approach. This applies in particular to the modeling of the physical effects as well as the technical implementation in robust optical systems for the production with ultrashort pulse lasers.


    Prof. Stefan Nolte (Jena)
  • Femtosecond inscribed chirped volume Bragg gratings
  • Volume Bragg gratings (VBGs) are a refractive index modulations within a transparent bulk material, having grating periods in the range of 1 µm, and act as a narrowband reflector. The gratings are inscribed by nonlinear absorption of femtosecond laser pulses, enabling the realization of VBGs in various types of glasses. Chirped VBGs, i.e. gratings with varying period over length, control the dispersive properties of the reflected signal, which can be utilized for pulse compression in chirped pulse amplification laser systems. The goal of this project is the realization of high power stable chirped VBGs by using femtosecond laser pulses to generate the refractive index modifications. The task is to further develop the inscription process from gratings with constant period to tailored profiles, providing excellent stability, ensuring the high power durability. Crucial is the control of the dispersive response for the successful application in pulse stretcher and compressor combinations.


    Prof. Gerhard Paulus (Jena)
  • Strong-field laser physics
  • A central goal of molecular physics is to steer the outcome of chemical reactions. Ultrashort laser pulses provide a powerful tool to study and also control molecular bonds on ultrashort time scales. However, the interaction of molecules with laser pulses is governed by the excitation of bound or unbound electronic states, while most conventional chemistry proceeds on the electronic ground state via excitation of vibrational levels. Using ultrashort IR lasers, we strive to investigate the largely unexplored field of ground-state photochemistry. To this end, we use highly sophisticated laser technology as well as an advanced ion beam apparatus with time- and position-resolved coincidence detection. Available topics range from instrumentation and laser technology to data analysis and theoretical simulations.

  • Nanoscale XUV imaging
  • XUV radiation has distinctive advantages for imaging, including resolution and element-specific contrast. We recently invented XUV coherence tomography (XCT), which enables non-destructive cross-sectional imaging with nanoscale resolution. Available topics include the combination with other lens-less imaging modalities, ultrafast nanoscale imaging, and multispectral imaging.

  • Precision X-ray polarimetry
  • We have developed X-ray polarimeters providing extinction ratios of better than 1E-10, by far the best in the world and also by far beyond of what is possible in the optical regime. The ultimate goal is to measure the birefringence of vacuum polarized by a strong laser – and we believe that we have sufficiently advanced X-ray polarimetry to do such an experiment at the European XFEL in the next years. However, precision X-ray polarimetry offers a large range of other research opportunities. One of these is X-ray polarization microscopy. Another, in collaboration with Professor Röhlsberger, X-ray quantum optics.


    Prof. Nina Rohringer (Hamburg)
  • Stochastic phase-space methods to treat time-dependent open many-body quantum systems in external laser fields
  • The advances in the fields of short-pulse laser and x-ray free-electron laser pulse creation allows probing of correlated and collective electron dynamics at its inherent attosecond timescale. State-of-the art methods to treat the interaction of ultrashort laser pulses with many-electron systems often resort to single-active electron approaches that are inherently unable to treat correlated many-body dynamics. On the other hand, computationally tractable time-dependent many-body theories, such as time-dependent density functional theory, the time-dependent Hartree Fock method, or time-dependent configuration interaction can account for electron correlation only to some limiting extent. This project focuses on the development of an alternative method to describe time-dependent many-body quantum systems. Recently, our group developed a theoretical framework that allows for a stochastic phase-space description of the time-dependent density matrix of an open many-body quantum system. In the project, the successful student should extend this formalism to treat correlated electron systems in external laser fields. Within this framework electron correlation beyond the Hartree-Fock level will be captured by stochastic processes defined by an appropriate noise correlation function, that has to be derived. Numerically, this will result in solving coupled stochastic differential equations, to sample the two-particle reduced electronic density matrix. We are looking for candidates with a strong interest in the development of novel theoretical methods, strong analytical skills and an interest in numerical implementation (programming).


    Prof. Claus Ropers (Göttingen)
  • Development of Ultrafast Low-Energy Electron Microscopy
  • In this Project, a new concept for real-space imaging of ultrafast dynamics at surfaces is to be developed. We plan to integrate a pulsed photoemission electron source with a low-energy electron microscope. This will allow for the surface-sensitive mapping of ultrafast structural phase transitions, and the generation and propagation of collective excitations.


    Dr. Vladislav Yakovlev (Munich)
  • Attosecond metrology
  • We study some of the fastest processes that accompany light-matter interaction. As our primary experimental approach, we investigate the light-controlled motion of charge carriers photoinjected within a time interval as short as a femtosecond. Combining our experimental and theoretical expertise, we develop novel methods for observing electron dynamics with attosecond temporal resolution. We also apply these methods to study processes that determine the fundamental speed limits of optoelectronics. For more information, see https://www.attoworld.de/atto-20.html

  • The coupling of physics and photonics for the development of new technologies, applicable for bio-medical sciences.
  • Leveraging the controlled electric field transients available at the Max Planck Institute of Quantum Optic, that push the limits of current laser technology, to achieve temporal confinement of the ionization of molecular systems, we aim for complete temporal separation between the excitation and the resulting radiation. We are investigating the effects of rapidly removing an electron from a molecule using an impulse-like intense laser field and studying the radiation emitted from the resulting molecular ion, within the IR, mid-IR and THz spectral ranges. This work should have impact within the fields of THz science, spectroscopy, and bio-medical sciences.


    Prof. Stefan Hell (Göttingen)
  • Far-Field Optical Imaging at Molecular Resolution
  • New concepts have radically overcome the longstanding limits to optical analysis of molecular systems. Optical resolutions of a few nano¬meters have been demonstrated, well beyond Abbe’s diffraction limit, for example with the recent MINFLUX concept (Science 355, 606-612 (2017)). This opens up entirely new experimental opportunities, breaking new ground in the study of macromolecules and beyond. The successful candidate will develop advanced optical instrumentation and investigate physical imaging conditions and resolution performance. Alternatively, a related project involving theoretical optical analysis and modelling can be offered. The candidate should have (or expect to complete soon) a Master’s or equivalent degree in Physics or Physical Chemistry or a comparable qualification.


    Prof. Ulrich Nienhaus (Karlsruhe)
  • Advanced Flourescence Microscopy
  • Stimulated emission depletion (STED) nanoscopy is a super-resolution fluorescence imaging technique to study biomolecular interactions in living systems at the highest possible temporal and spatial resolution. In this research, STED nanoscopy-based instrumentation will be advanced through implementation of ultrafast laser beam scanners and adaptive optics for suppression of aberrations. Moreover, novel data analysis tools based on single particle tracking and spatial/temporal correlations of pixel intensities will be developed and used for a range of biophysical experiments on living systems (cells, tissues organisms).


    Prof. Stefan Nolte (Jena)
  • Fs-laser induced cross-linking of corneal tissue
  • This highly interdisciplinary project is a collaboration with physicians and engineers of the universities in Göttingen and Jena to evaluate treatment scenarios using fs-laser induced cross-linking of corneal tissue. Possible applications are the treatment of keratoconus, or even refractive correction of myopia. Currently, the method of UV (A)-riboflavin crosslinking is used to stabilize the cornea in the keratoconus. Riboflavin is applied locally and cross-linked by UV (A) radiation. Yet, the precision of this procedure is low, and the exclusive treatment of diseased areas is not possible. In this project, fs-lasers should be used for the cross-linking of corneal collagen fibres. Using a high-speed scanner system, the focal spot of the fs-laser can be precisely controlled on the corneal surface allowing for a selective treatment of diseased areas.


    Prof. Jürgen Popp (Jena)
  • Coherent biomedical Raman Imaging by means of ultrafast tunable laser sources
  • Novel Laser based techniques for imaging and spectroscopy, e.g., optical coherence tomography or coherent Raman imaging, are highly promising for biomedical applications. While techniques like stimulated Raman scattering put highest demands on the laser specifications, e.g., in terms of tuning range, tuning speed, bandwidth or noise, for successful clinical translation the laser systems have to be at the same time robust, compact and easy to use. In the group of Prof. Limpert custom-designed ultrafast fiber lasers are developed. Therefore, the aim of this work is to explore, adapt and apply novel laser concepts from the research group of Prof. Limpert (e.g., Fourier-domain mode locked lasers, four wave mixing frequency conversion) in biomedical imaging and spectroscopy, like hyperspectral coherent Raman imaging in the vibrational fingerprint region or multiplex coherent imaging of Raman tags. Furthermore, novel CARS excitation schemes for super resolution vibrational imaging beyond the Abbe limit utilizing the aforementioned laser sources should be explored.


    Dr. Vladislav Yakovlev (Munich)
  • Attosecond metrology
  • We study some of the fastest processes that accompany light-matter interaction. As our primary experimental approach, we investigate the light-controlled motion of charge carriers photoinjected within a time interval as short as a femtosecond. Combining our experimental and theoretical expertise, we develop novel methods for observing electron dynamics with attosecond temporal resolution. We also apply these methods to study processes that determine the fundamental speed limits of optoelectronics. For more information, see https://www.attoworld.de/atto-20.html


    Prof. Nicolas Joly (Erlangen)
  • Photonic crystal fibres under pressure, one, two, three photons sources for quantum optics Photonics production

  • Prof. Bernhard Schmauß (Erlangen)
  • Optical frequency reflectometry based distributed spectroscopy

  • Dr. Birgit Stiller (Erlangen)
  • Light-sound interactions in the quantum domain
  • Optical waves interacting with acoustic or mechanic vibrations is a fascinating phenomenon because it links two very different domains in terms of frequency, velocity, dissipation and other properties. We explore these interactions experimentally at the classical and quantum level with suitably engineered microstructured fibres and nanowaveguides to manipulate, in this way, light states. Possible applications are a temporal memory for light, signal processing, high-sensitivity sensing and many more. The aim of this experimental PhD project is to explore the concepts of entanglement and squeezing via optoacoustic interaction. The topic is situated at the interface of quantum optics, nonlinear optics and quantum information processing. It involves conception and setup of fiber optical and chip-based experiments, photonic design (with option of fabrication) and numerical analysis and interpretation within the rich theoretical background.


    Dr. Hanieh Fattahi (Erlangen)
  • Generation of high energy, sub-cycle pulses
  • In this project, we employ state of the art high-energy, Yb:YAG thin disk lasers combined with broadband optical parametric amplifier and coherent field synthesis to generate sub-cycle pulses, or the so called light transients. High energy, optimised light transients allow to control nonlinear phenomena in sub-cycle regime (1,2). A good experience on developing lasers, handling ultrashort pulses, Labview and Matlab is beneficial for this position. 1."Multi-octave, CEP-stable source for high-energy field synthesis” A Alismail, H Wang, G Barbiero, …, H. Fattahi, Science advances 6 (7), eaax3408, 2020 2."Third-generation femtosecond technology", H Fattahi, HG Barros, M Gorjan, …, F. Krausz, Optica 1 (1), 45-63, 2014


    Prof. Franz Kärtner (Hamburg)
  • Cryogenic Lasers at 1 and 2 micron
  • We develop novel high average power and high energy laser systems at both 1 mciron wavelength such as Yb:YAG and Yb:YLF as well as in the 2 micron region with Tm:YLF and Ho:YLF. Cryogenic cooling results in a significant advantage in the thermo-optical and thermo-mechanical properties of laser materials resulting in significant advantages in power and energy handling. The lasers are applied to drive optical parametric sources, high energy THz generation and direct laser acceleration in the MID-IR within the international accelerator on chip program (ACHIP). Direct laser acceleration of relativistic electron beams with dielectric structures or pursued jointly with DESY’s accelerator division.


    Prof. Matthias Kling (Munich)
  • Attosecond imaging and spectroscopy of light-induced dynamics in molecules and nanostructures
  • We are interested in ultrafast correlated and collective electron dynamics that unfold when complex materials are exposed to intense, ultrashort laser fields. In particular this includes the attosecond control and tracing of strongly coupled electron-nuclear dynamics in quantum systems such as molecules, and of collective electron dynamics in nanostructured materials, and lightwave-driven petahertz (nano)electronics. We develop and use multi-dimensional imaging techniques in conjunction with (attosecond) pump-probe experiments to gain detailed insight into the dynamics from the interaction of these materials with near-single cycle laser fields of typically attosecond to femtosecond duration. We actively push the theoretical modeling of the rather complex multi-charge dynamics, which are partly carried out in our group using Monte-Carlo simulations with more intricate models within collaborations.


    Prof. Jens Limpert (Jena)
  • Multi-pulse nonlinear pulse compression
  • Nonlinear pulse compression has become an irreplaceable technology that allows laser pulses from high-power laser systems to be temporally shortened so that they are suitable for numerous scientific applications in the field of high-field physics. This process can be realized either in gas-filled hollow-core fibers or in multi-pass cells. While both techniques have demonstrated massive performance advances in recent years, physical and practical limitations still pose a challenge. Today, more powerful laser systems are available than what these setups can handle. Parallelization in the form of coherent pulse combination has already been successfully applied for performance scaling of laser amplifiers. This concept should now be applied to nonlinear compression, especially focused on nonlinear multi-pass cells, which will pave a new path towards laser systems emitting few-cycle, high energy pulses at high average powers. The short pulse durations and associated broad optical bandwidths pose unique challenge, ranging from optics to control electronics. These will have to be addressed by novel approaches that will be developed in the frame of this thesis.


    Dr. Falk Eilenberger (Jena)
  • Functionalization of Photonic Nanocircuits with 2D-Materials
  • Semiconducting 2D-Materials are a new and exciting material for Photonics. They exhibit unusually strong light matter interaction, including nonlinear effects, single photon emitters, and collective quantum behaviour. Moreover, they can be grown on as crystals structured substrates and can be used to functionalize optical nanostructures and circuits. Possible research topics include the growth of 2D-Materials on nanowaveguides and inside photonic crystal fibers, the characterization of light matter interaction therein and the development of applications in optical sensing and quantum technology.


    Prof. Stefan Hell (Göttingen)
  • Far-Field Optical Imaging at Molecular Resolution
  • New concepts have radically overcome the longstanding limits to optical analysis of molecular systems. Optical resolutions of a few nano¬meters have been demonstrated, well beyond Abbe’s diffraction limit, for example with the recent MINFLUX concept (Science 355, 606-612 (2017)). This opens up entirely new experimental opportunities, breaking new ground in the study of macromolecules and beyond. The successful candidate will develop advanced optical instrumentation and investigate physical imaging conditions and resolution performance. Alternatively, a related project involving theoretical optical analysis and modelling can be offered. The candidate should have (or expect to complete soon) a Master’s or equivalent degree in Physics or Physical Chemistry or a comparable qualification.


    Prof. Franz Kärtner (Hamburg)
  • Femtosecond Laser on a Chip
  • We explore and advance nonlinear optical technologies for realizing an integrated femtosecond laser in a silicon photonics process. The laser should provide optical pulse trains with quantum limited timing jitter on the single femtosecond range and below. The nonlinear processes enable sub-shot noise photon statistics, which shall be modelled and characterized experimentally. The project can be theoretical and/and experimental depending on preference.


    Prof. Matthias Kling (Munich)
  • Attosecond imaging and spectroscopy of light-induced dynamics in molecules and nanostructures
  • We are interested in ultrafast correlated and collective electron dynamics that unfold when complex materials are exposed to intense, ultrashort laser fields. In particular this includes the attosecond control and tracing of strongly coupled electron-nuclear dynamics in quantum systems such as molecules, and of collective electron dynamics in nanostructured materials, and lightwave-driven petahertz (nano)electronics. We develop and use multi-dimensional imaging techniques in conjunction with (attosecond) pump-probe experiments to gain detailed insight into the dynamics from the interaction of these materials with near-single cycle laser fields of typically attosecond to femtosecond duration. We actively push the theoretical modeling of the rather complex multi-charge dynamics, which are partly carried out in our group using Monte-Carlo simulations with more intricate models within collaborations.


    Prof. Peter Loosen (Aachen)

  • Design, realization, and characterization of metaoptics in the VIS to NIR-spectrum
  • Metaoptics are evolving as a competitor to conventional optics by offering more design freedom and new resulting functionalities. One remaining obstacle still is the cost-efficient fabrication of these nanostructured surfaces that is so far mainly realized by time-expensive electron beam lithography. Within this thesis, the lab-based interference lithography with extreme-ultraviolet radiation which has been developed at the chair TOS shall be extended from periodic structures to quasi-periodic and even aperiodic structures. Main tasks are the design of compatible metaatom arrangements, the creation and functionalization of those structures and the subsequent characterization of the metaoptics’ performance at visible (VIS) and near-infrared (NIR) wavelengths serving as a basis for an industrial evolution in optics.


  • Design of EUV-systems for processing and characterization of nanostructures
  • In the course of the industrial implementation of extreme-ultraviolet (EUV) radiation for the realization of next-gen microchips, we are developing compact lab-based EUV-systems. These unique systems are used to support industrial applications like photoresist characterization or critical dimension metrology both on the nanoscale. Within this thesis, existing and new experimental systems shall be (re-) designed and upgraded to keep up the pace with the industrial developments. The tasks also include the development and evaluation of efficient algorithms to predict intensity distributions or reconstruct nanoscale structures by the analysis of their diffraction pattern for inline process control.


    Prof. Ulrich Nienhaus (Karlsruhe)
  • Advanced Flourescence Microscopy
  • Stimulated emission depletion (STED) nanoscopy is a super-resolution fluorescence imaging technique to study biomolecular interactions in living systems at the highest possible temporal and spatial resolution. In this research, STED nanoscopy-based instrumentation will be advanced through implementation of ultrafast laser beam scanners and adaptive optics for suppression of aberrations. Moreover, novel data analysis tools based on single particle tracking and spatial/temporal correlations of pixel intensities will be developed and used for a range of biophysical experiments on living systems (cells, tissues organisms).


    Prof. Stefan Nolte (Jena)
  • Spin-orbit photonics in inhomogeneous anisotropic media
  • In standard photonics light propagation is dictated by the refractive index gradient: photons behave as massive quantum particles under the action of a potential equal to the refractive index. Nonetheless, the behavior of photons can be far more complex, especially in the presence of exotic light-matter interaction. Here we aim to investigate the strong interaction between the spin (i.e., the light polarization) and the orbital (i.e., the wave vector) occurring when photons propagate in inhomogeneous anisotropic materials. In this regime light evolution recalls the propagation of charged particles in a magnetic field, and new effects are observed due to the gradients in the Pancharatnam-Berry phase. The fundamental nature and possible applications of spin-orbit phenomena will be both pursued, in the linear and nonlinear regime, including materials such as liquid crystals, light-written nanogratings in glass, two-photon polymerized structures and biased nanoguides in Lithium Niobate.


    Prof. Thomas Pertsch (Jena)
  • Nanoscale photon control for next generation ultrafast integrated quantum systems
  • Nanosized quantum emitters are the basis of many quantum photonic circuits. However due to the size mismatch between the nanosized emitters and the micron scale radiation fields, their coupling to propagating electro-magnetic waves is weak and difficult to control. Therefore, exploiting strongly localized nearfields of nano-resonators or plasmonic elements is considered to be a key element for the realization of strong coupling. Scanning near-field optical microscopy (SNOM) is a powerful technique to measure and study simultaneously the architecture of nanostructures and their electromagnetic near fields. Among the different types of SNOMs, the scattering pseudo-heterodyne SNOM (ps-het SNOM) offers two main advantages: high resolution in topographical and optical images by employing sharp cantilever tips and simultaneous detection of field intensity and phase by exploiting lock-in detection methods and interferometry. In this PhD project, we aim to take the performance of ps-het SNOM-based near-field detection and control to the next level with the vision to realize strong coupling to quantum emitters, as e.g. vacancy centers, quantum dots, quantum dots, lanthanide nanoparticles, and emission centers in atomically thin membranes of MoS2. To achieve this goal we study a new generation of high-performance plasmonic tips, which promise to provide unprecedented performance parameters. As a first step, the SNOM tips' performance parameters are to be evaluated by exploring the tip's interaction with different quantum systems. To explore the spectral and temporal characteristics of the quantum systems, a superfocusing SNOM setup will be combined with a time correlated single photon counting system and a single photon sensitive optical spectrometer. After establishing stable measurement methods and skills, we want to apply this tool to the in depths investigation of the interaction of the nano-sized quantum systems with plasmonic and dielectric nano-antennas. Besides experimental characterization, analytical and computational modeling shall be carried out to understand the complex behavior of the quantum emitters and their interaction with the tips.


  • Spatiotemporal dynamics of nano-scale light-matter interactions in metasurfaces and atomic membranes
  • The control and characterization of light on length scales shorter than the diffraction limit (~500 nm) requires shaping or probing of the photonic states by nano-scale matter. Therefore, basically all nanooptical effects are coupled states of light and excited matter. Hence, the exploration of optics down to the nanoscale requires detailed knowledge about strong light-matter interaction at these ultrashort length scales. This interaction typically concerns the electronic states and happens on ultrashort time scales of a few femtoseconds. The experimental observation of such effects hence requires tools probing simultaneously the electronic matter states and the photonic states with nanometer spatial and femtosecond temporal resolution. The aim of this PhD project is to study such ultrafast nanoscale dynamics in semiconductor metasurfaces, which are hybridized with plasmonic antennas, nanowires, and atomic membranes like graphene or MoS2. To achieve this goal new experimental techniques with unprecedented temporal and spatial have to developed. Besides scanning nearfield optical microscopy (SNOM), laser driven photoemission electron microscopy (PEEM) is such a technique, which probes directly the electronic excitation of matter with the spatial resolution of an electron microscope. Temporal resolution is obtained by triggering the photoemission by few-cycle laser pulses. These ultra-short laser pulses give access to dynamical processes, inaccessible to electronic measurement systems. Laser driven PEEM is thus an ideal probe to study the photo-induced electron dynamics in the building blocks of photonic nanosystems. A typical PhD project will combine advanced instrumentation of fs lasers and ultra-high vacuum systems for electron microscopy with the physics of several novel quantum systems and metasurfaces.


  • Machine learning based design of nanostructured photonic metamaterials
  • Photonic metamaterials are a novel class of artificial matter consisting of building blocks, which are derived from sophisticated nanotechnologies and which have a mesoscopic size smaller than the wavelength of light. Metamaterials promise to obtain complete control over all classical, nonlinear, and quantum-optical properties characterizing light propagation. By designing the metamaterials´ unit cells one can tailor the linear and nonlinear light propagation in such media beyond the limits given by natural occurring materials. A focus of the PhD topic will lie in machine learning based algorithms for inverse design processes of novel nanomaterials. The project will evolve along the lines of simulation-based design of metamaterials, their practical realization using state-of-the-art lithography-based nanotechnologies, as well as their experimental characterization to close the loop for application-oriented optimization of resulting electromagnetic parameters.


    Prof. Carsten Rockstuhl (Karlsruhe)
  • Theoretical and Numerical Nanooptics
  • We study by analytical and numerical means the interaction of light in the linear, nonlinear, and quantum regime with nanostructured materials such as metals, semiconductors, dielectrics, or also molecular materials and explore applications thereof with different partners. Referential examples for such applications are, e.g., in the field of wave front shaping in integrated optical systems or for quantum sensing devices. We have activities in the field of plasmonics, optical nanoantannas, metamaterials and metasurfaces, computational material design (also known as solving the inverse problem), and quantum optics at the nanoscale in place and are currently seeking a PhD student to reinforce our team.


    Prof. Claus Ropers (Göttingen)
  • Development of Ultrafast Low-Energy Electron Microscopy
  • In this Project, a new concept for real-space imaging of ultrafast dynamics at surfaces is to be developed. We plan to integrate a pulsed photoemission electron source with a low-energy electron microscope. This will allow for the surface-sensitive mapping of ultrafast structural phase transitions, and the generation and propagation of collective excitations.


    Dr. Birgit Stiller (Erlangen)
  • Light-sound interactions in the quantum domain
  • Optical waves interacting with acoustic or mechanic vibrations is a fascinating phenomenon because it links two very different domains in terms of frequency, velocity, dissipation and other properties. We explore these interactions experimentally at the classical and quantum level with suitably engineered microstructured fibres and nanowaveguides to manipulate, in this way, light states. Possible applications are a temporal memory for light, signal processing, high-sensitivity sensing and many more. The aim of this experimental PhD project is to explore the concepts of entanglement and squeezing via optoacoustic interaction. The topic is situated at the interface of quantum optics, nonlinear optics and quantum information processing. It involves conception and setup of fiber optical and chip-based experiments, photonic design (with option of fabrication) and numerical analysis and interpretation within the rich theoretical background.


    Prof. Peter Loosen (Aachen)

  • Novel concepts for high-power digital laser beam shaping
  • Numerous approaches for dynamic beam shaping of laser radiation already exist, such as spatial light modulators (SLMs). A common problem is that the optical elements for beam shaping are not applicable for the high-power range (> 500 W). Especially in the field of laser material processing like laser hardening or laser powder bed fusion (LPBF), high laser powers are needed with a simultaneous increasing demand for individual beam shaping to optimize the process result. For this reason, we are exploring possibilities to make highly dynamic beam shaping accessible for high power applications. We are working on the optimization of existing optical elements as well as on fundamentally new approaches.

  • Computational methods for application adapted intensity distributions
  • In many application areas such as automotive or architectural lighting, freeform optics with many degrees of freedom enable complex illumination. The surfaces of these optics are shaped to specifically redirect the light so that in total a prescribed pattern of dark and bright areas on a target surface is obtained that might e.g. be completely homogeneous within a given area or form an image (of a person, a place of interest etc.). As the surfaces and their mathematical descriptions are complex, numerical freeform optics design strategies are required. We developed several algorithms for the design of freeform optics for various optimization goals. In the next years, research will focus on increasing the robustness of freeform optics, on using coherent light sources (lasers) and on enhancing the flexibility regarding wavelength as well as thermal loads.

  • Multi-physics modelling of metaoptics
  • Flat metaoptics consist of geometries with extents in the size of the wavelength that are arranged in a two-dimensional array on a substrate. By employing wave optical effects that cannot be achieved with classical optical elements, completely new functional behavior is obtained, e.g. a high numerical aperture (NA) or so-called anomalous reflection or refraction which goes beyond Snell’s law and the law of reflection, respectively. We develop methods that simulate the behavior of metaoptics and other small-size components using wave optical approaches. To analyze the functionality of metaoptics in macroscale setups and in combination with classical optical elements, wave optical models are combined with raytracing and rendering techniques. Within the planned project, computational methods are developed to design metaoptics for various applications such as augmented reality, laser beam shaping, and general lighting.


    Prof. Bernhard Schmauß (Erlangen)
  • Optical frequency reflectometry based distributed spectroscopy

  • Prof. Dr. Christine Silberhorn (Paderborn)
  • Multi-outcome quantum pulse gate for time-frequency high-dimensional quantum key distribution
  • High-dimensional quantum key distribution (HDQKD) promises an increase in both the security and secret key rates by going beyond a traditional qubit encoding. This excludes the use of polarization and - if we additionally require compatibility with integrated optics - spatial encodings. Information can be encoded in the time-frequency domain. Our group has shown that a quantum pulse gate (QPG) implements projective measurements onto arbitrary time-frequency bases. Yet, the current device design is limited to only one single measurement outcome; a limitation that makes it unsuitable for HDQKD. The goal of this project is to implement a multi-outcome QPG for time-frequency HDQKD with more than 10 dimensions. The research strategy will combine nonlinearity engineering, resonant structures, and temporal multiplexing, and will yield a high-performing plug-and-play device that is compatible with single-mode fibre.


    Prof. Andreas Tünnermann (Jena)
  • High-dimensional quantum communication in tailored optical fibers
  • Path-encoded quantum bits have provided the basis for a myriad of proof-of-concept experiments in photonic quantum computing in the laboratory. As applications of quantum computers venture into the realm of distributed quantum information processing, a key challenge is the transmission of such states over long distances. Recent developments in multi-core fibers and tailored few-mode fibers would allow vast amounts of quantum information to be transmitted between distributed parties in a manner that is compatible with photonic quantum computing platforms.

  • High-dimensional quantum communication in long-distance free-space and fiber links
  • Increasing the throughput of quantum communication links is a key technological challenge on the way to a global quantum internet. Research topics include the development of field- and space-ready quantum hardware, broadband quantum key distribution systems based on time- and frequency-encoded quantum states, and the integration of quantum communication systems into a long-haul optical fiber link between Jena and Erfurt and/or a local free-space optical link.


    Dr. Falk Eilenberger (Jena)
  • Single Photon Sources for Quantum Communication and Quantum Computing
  • Single Photon Sources are among the key elements in Quantum Communication networks and will play a major role in the interconnection of quantum computers. We investigate single photon source in 2D-Materials: such sources have supreme photon quality, are very robust and have the potential to be integrated in photonic appliances. Possible research topics include the development of a quantum payload for a cube satellite mission, experimental investigations of theories in quantum gravity and the integration of 2D materials in advanced optical systems.



    Dr. Maria Chekhova (Erlangen-Nürnberg)
  • Third-order parametric down-conversion
  • The goal is to experimentally observe a new nonlinear optical effect: direct decay of a photon in three, the inverse to the third harmonic generation. This effect, called third-order parametric down-conversion, is an upgrade of spontaneous parametric down-conversion (SPDC). It is far more unusual and interesting than SPDC: it results in quantum states of light with negative Wigner functions and it offers a realization of a cubic quantum gate, highly demanded in quantum information. Despite many theoretical works and several experimental attempts with nonlinear crystals, waveguides, and fibers, it has been not observed so far. In this PhD project the concept is to use a new class of materials, namely ultrathin layers with giant cubic nonlinearities (semiconductors, chalcogenide glass, metasurfaces) where phase matching will be not needed.

  • Loss-tolerant quantum imaging with twin beams
  • One of the ways to enhance signal-to-noise ratio in imaging is to illuminate an object with twin beams, for which the photon numbers are correlated. Such twin beams are produced at the output of a nonlinear crystal through high-gain parametric down-conversion. However, this technique is useless if the detection efficiency is not extremely high. The project aims at further developing this technique by adding phase sensitive parametric amplification of the image, which will make the imaging tolerant to any loss and therefore suitable for ‘difficult’ spectral ranges like IR and terahertz.


    Prof. Nicolas Joly (Erlangen)
  • Photonic crystal fibres under pressure, one, two, three photons sources for quantum optics

  • Prof. Gerd Leuchs (Erlangen)
  • Interaction of light with single atoms/ions, optically trapped nano-particles and gaseous nonlinear optical media
  • The dynamics of the interaction of light and matter depends sensitively on the properties of the light field. When focusing light, the electric field in the focus is maximized by sending in linear-dipole radiation from the full solid angle, optimizing the efficiency of the interaction with dipole-like matter. We offer topics for PhD theses centered around this scenario, in particular (1) the interaction of light with single atoms/ions, (2) optically trapped nano-particles as well as (3) gaseous nonlinear optical media. The topics relate to fundamental questions in classical and quantum optics and to the development of optical quantum technologies.


    Prof. Thomas Pertsch (Jena)
  • Nanoscale integrated quantum photonics
  • Nanoscale waveguides in lithium niobate on insulator systems are an emerging platform for integrated optics that offers unrivalled properties like small absorption losses in a wide spectral range, high optical nonlinearities, and the ability for ultrafast modulation of material properties. Based on these exceptional properties, a number of basic elements for integrated optics, e.g. low-loss waveguides, fast modulators, and nonlinear frequency converters have been demonstrated. All these demonstrations used waveguides with cross-sections in the range of a few hundred nm, showing the large potential of this platform for high-performance integrated optics that can realize complex photonic functionalities in very small devices. We aim to use this platform to move quantum optics to the nanoscale by implementing sources for photonic quantum states, optical elements to modify and control these quantum states as well as single-photon detectors in a single optical chip. This will enable to realize different quantum functionalities in lithium niobate nano-waveguides, e.g. quantum-enhanced sensing devices, sources, and receivers for quantum communication, or circuits that implement optical quantum computing. The project comprises the development, optimization, and test of individual quantum elements in such circuits, the implementation of basic quantum interference experiments to gauge the performance of complex lithium niobate quantum circuits and the design and realization of large-scale circuits that perform applicable functionalities.


    Prof. Nina Rohringer (Hamburg)
  • Source of entangled photon pairs and triplets via parametric down conversion in photonic crystals: opportunities from many-beam diffraction
  • Generation of entangled-photon pairs via parametric down-conversion (PDC) is an essential ingredient of numerous quantum-optics and quantum-information setups. To achieve the PDC generation, nonlinear response of the crystal in combination with phase-matching conditions is employed. The generation of entangled photon-triplets (for example, Greenberger–Horne–Zeilinger states) would provide further opportunities, however is even more challenging due to higher nonlinearities needed and further restrictions on phase-matching. In the current project, we propose to use photonic crystals (structures with artificially created spatial periodicity) to enhance the generation of PDC photons. Namely, we aim at a systematic exploration of the additional degrees of freedom emerging thanks to artificial periodicity (orientation of reciprocal lattice vectors) that can be used to steer the phase-matching conditions. The shaping of the electromagnetic field in the periodic structures (many-beam diffraction) was well-studied for x-rays and natural crystals. In this project, we aim at transferring the concepts from x-ray crystallography to photonic-crystals optics in order to find opportunities for enhanced production of entangled photons.


    Prof. Dr. Christine Silberhorn (Paderborn)
  • Multi-outcome quantum pulse gate for time-frequency high-dimensional quantum key distribution
  • High-dimensional quantum key distribution (HDQKD) promises an increase in both the security and secret key rates by going beyond a traditional qubit encoding. This excludes the use of polarization and - if we additionally require compatibility with integrated optics - spatial encodings. Information can be encoded in the time-frequency domain. Our group has shown that a quantum pulse gate (QPG) implements projective measurements onto arbitrary time-frequency bases. Yet, the current device design is limited to only one single measurement outcome; a limitation that makes it unsuitable for HDQKD. The goal of this project is to implement a multi-outcome QPG for time-frequency HDQKD with more than 10 dimensions. The research strategy will combine nonlinearity engineering, resonant structures, and temporal multiplexing, and will yield a high-performing plug-and-play device that is compatible with single-mode fibre.

  • Development of integrated nonlinear optical and electro-optical devices exploiting counter-propagating interactions in periodically poled waveguides with ultra-short poling periods
  • Future progress in the development in the emerging field of optical quantum technologies requires compact and miniaturized solutions for quantum circuits. Lithium niobate is proven to be a well-established material platform for numerous integrated quantum optical circuits. Recent progress in the technology for the fabrication of specifically tailored domain patterns with ultra-short poling periods will complement the portfolio of integrated functional elements in LiNbO3 for quantum applications. This project aims on the development of integrated nonlinear optical and electro-optical devices exploiting counter-propagating interactions in periodically poled waveguides with ultra-short poling periods. Among them can be photon-pair sources for the generation of decorrelated quantum states and electro-optically tuneable mirrors and polarization converters.


    Dr. Birgit Stiller (Erlangen)
  • Light-sound interactions in the quantum domain
  • Optical waves interacting with acoustic or mechanic vibrations is a fascinating phenomenon because it links two very different domains in terms of frequency, velocity, dissipation and other properties. We explore these interactions experimentally at the classical and quantum level with suitably engineered microstructured fibres and nanowaveguides to manipulate, in this way, light states. Possible applications are a temporal memory for light, signal processing, high-sensitivity sensing and many more. The aim of this experimental PhD project is to explore the concepts of entanglement and squeezing via optoacoustic interaction. The topic is situated at the interface of quantum optics, nonlinear optics and quantum information processing. It involves conception and setup of fiber optical and chip-based experiments, photonic design (with option of fabrication) and numerical analysis and interpretation within the rich theoretical background.


    Prof. Andreas Tünnermann (Jena)
  • High-dimensional quantum Comb Entanglement
  • High-dimensional quantum states (known as qudits, with dimension d>2) allow storing and processing more information than the 2-dimensional qubits, and have proven to make quantum information processing more resistant to noise. Encoding such states in discrete frequency modes has key advantages, such as huge parallelization, the possibility to implement universal quantum gates, as well as compatibility with standard telecommunication components. Possible research topics include the development of frequency-entangled and squeezed light sources, novel methods to detect and manipulate frequency-entangled states using electrooptic modulators and dispersive elements, and the application of frequency-entanglement in quantum sensing and information processing.

  • Quantum information processing with spatially structured photons
  • The structuring of the wavefront of photons allows complex entangled quantum states to be generated and promises quantum information processing with improved capacity. Research topics include engineering quantum states using diffractive optical elements and metamaterials, the propagation of spatial modes through atmospheric free-space links, mode correction of photons using machine learning, and the application of spatial quantum states in quantum information processing.

  • Development of squeezed light sources for photonic quantum simulation and sensing applications
  • Squeezed states of light are a key resource in photonic quantum computing and quantum sensing. Possible research topics include tailoring the spectral properties of squeezed states of light, manipulation and generation of complex continuously-variable quantum states (Schrödinger cat states, Entangled Coherent States, NOON States), and the application of non-classical light sources in quantum ranging or photonic quantum computing.

  • Development of quantum spectroscopy based on non-linear interferometers
  • Similar to microscopy, the spectroscopic analysis of substances is a crucial process in life and material sciences. One of the main obstacles in application is the lack of high-efficient detectors in vital spectral ranges. For instance, molecular fingerprint spectroscopy in the MIR suffers from poor detection efficiencies provided by InGaAs cameras. The utilization of correlated photon pairs and interferometric settings allows the achievement of spectroscopy in extreme spectral ranges while efficiently detecting visible light only. In addition, multi-photon spectroscopy of photosensitive substances becomes more efficient when harnessing photon pairs. In this project, you will develop and implement novel approaches for quantum spectroscopy. The work will involve the theoretical modelling, experimental proof-of-concept realization, and transfer into applicable devices. Particular interest should be spent on benchmarking and comparison with standard spectroscopy techniques and demonstrating the feasibility and advantage for extreme wavelengths applications.

  • Investigation of higher-order events and higher-order correlations in non-linear interferometers
  • Microscopy is a versatile tool without which modern life science and material analysis could not exist. However, there are intrinsic limitations in the interplay of the wavelength for investigation, the available detection efficiency in that spectral range and the acceptable photon dose for the specimen. Based on quantum optical effects in non-linear interferometers one can overcome some of these restrictions by allowing the imaging in extreme wavelength ranges while detecting visible light only. So far, all implementations relied on two-photon events and two-photon correlations. Your task will be to investigate the impact of high-order photon events and high-order correlations in order to increase spatial resolution, sensitivity, and precision. Moreover, your work will include the analyze the transition from the quantum regime towards the classical regime, where stimulated rather than spontaneous conversion processes are dominating.

  • Interaction of non-classical states of light with matter within the framework of entangled two-photon absorption and fluorescence microscopy
  • Two-photon microscopy is a special form of laser scanning microscopy that uses the non-linear effects of two-photon absorption. Since both photons are correlated (in energy, impulse, time and room), the fluorescence depends only linearly on the excitation intensity. Furthermore, the phototoxicity is minimized due to the single photon level. However, proof-of-principle experiments and fundamental questions regarding light matter interaction in a quantum mechanical description are still open. Your tasks include to address the fundamental modelling of non-classical light interaction with molecular structures to deduct strategies for enhancement of entangled two-photon absorption processes as well as the experimental implementation.



    Dr. Hanieh Fattahi (Erlangen)
  • Generation of high energy, sub-cycle pulses
  • In this project, we employ state of the art high-energy, Yb:YAG thin disk lasers combined with broadband optical parametric amplifier and coherent field synthesis to generate sub-cycle pulses, or the so called light transients. High energy, optimised light transients allow to control nonlinear phenomena in sub-cycle regime (1,2). A good experience on developing lasers, handling ultrashort pulses, Labview and Matlab is beneficial for this position. 1."Multi-octave, CEP-stable source for high-energy field synthesis” A Alismail, H Wang, G Barbiero, …, H. Fattahi, Science advances 6 (7), eaax3408, 2020 2."Third-generation femtosecond technology", H Fattahi, HG Barros, M Gorjan, …, F. Krausz, Optica 1 (1), 45-63, 2014


    Prof. Peter Hommelhoff (Erlangen)
  • Particle acceleration on a nanophotonic chip
  • Before particle acceleration comes transport. Transport through an accelerator structure means that a particle beam can be actively steered through the required elements needed to build a particle accelerator. This is what we have achieved through a nanophotonic channel (Nature 2021). Based on this, we are now ready to build the particle accelerator on a chip. Various topics have to be tackled for this, ranging from electron beam simulation driven with the optical nearfields, via structure optimization to the integration of the optics to power the structure.
    * Building the accelerator on a naonphotonic chip
    * Next to acceleration, these structures also allow generation of attosecond electron bunches, which we will use for various laser pump--electron probe experiments.


  • Ultrafast coherent electron dynamics in solids: towards petahertz electronics
  • With phase-controlled laser fields, we have driven electrons inside of graphene fully coherently. We have demonstrated Landau-Zener-Stückelberg interferometry, so subsequent coherent Landau-Zener transitions, leading to a net current (Nature 2017). Based on this, we have further demonstrated more complex coherent current control driven on optical time scales. These insights allow us to now move towards electronics on optical timescales, i.e., petahertz electronics. Both the fundamental physics in various materials and at heterostructures as well as initial building blocks are on our research agenda.


    Prof. Franz Kärtner (Hamburg)
  • Efficient THz generation
  • We explore different ways to overcome the Manley-Rowe limit for THz generation with lasers through optical rectification through cascading in periodically poled nonlinear materials. Students will get familiar with the use of high energy short pulse lasers in driving strongly nonlinear processes. Eventually conversion beyond several percent from optical to THz is realized. The high energy THz pulses are used ifor THz acceleration.


  • Strong-field Physics / Attosecond Science
  • We us sub-cycle parametric waveform synthesis to generate and control isolated attosecond pulses in the EUV to soft-x-ray region for attosecond transient absorption spectroscopy and apply this technique to various fundamental processes such as radiolysis in water, chemical processes in energy conversion and controlled attosecond electron wave packet generation.


    Prof. Matthias Kling (Munich)
  • Attosecond imaging and spectroscopy of light-induced dynamics in molecules and nanostructures
  • We are interested in ultrafast correlated and collective electron dynamics that unfold when complex materials are exposed to intense, ultrashort laser fields. In particular this includes the attosecond control and tracing of strongly coupled electron-nuclear dynamics in quantum systems such as molecules, and of collective electron dynamics in nanostructured materials, and lightwave-driven petahertz (nano)electronics. We develop and use multi-dimensional imaging techniques in conjunction with (attosecond) pump-probe experiments to gain detailed insight into the dynamics from the interaction of these materials with near-single cycle laser fields of typically attosecond to femtosecond duration. We actively push the theoretical modeling of the rather complex multi-charge dynamics, which are partly carried out in our group using Monte-Carlo simulations with more intricate models within collaborations.


    Prof. Stefan Nolte (Jena)
  • Femtosecond inscribed chirped volume Bragg gratings
  • Volume Bragg gratings (VBGs) are a refractive index modulations within a transparent bulk material, having grating periods in the range of 1 µm, and act as a narrowband reflector. The gratings are inscribed by nonlinear absorption of femtosecond laser pulses, enabling the realization of VBGs in various types of glasses. Chirped VBGs, i.e. gratings with varying period over length, control the dispersive properties of the reflected signal, which can be utilized for pulse compression in chirped pulse amplification laser systems. The goal of this project is the realization of high power stable chirped VBGs by using femtosecond laser pulses to generate the refractive index modifications. The task is to further develop the inscription process from gratings with constant period to tailored profiles, providing excellent stability, ensuring the high power durability. Crucial is the control of the dispersive response for the successful application in pulse stretcher and compressor combinations.

  • Spin-orbit photonics in inhomogeneous anisotropic media
  • In standard photonics light propagation is dictated by the refractive index gradient: photons behave as massive quantum particles under the action of a potential equal to the refractive index. Nonetheless, the behavior of photons can be far more complex, especially in the presence of exotic light-matter interaction. Here we aim to investigate the strong interaction between the spin (i.e., the light polarization) and the orbital (i.e., the wave vector) occurring when photons propagate in inhomogeneous anisotropic materials. In this regime light evolution recalls the propagation of charged particles in a magnetic field, and new effects are observed due to the gradients in the Pancharatnam-Berry phase. The fundamental nature and possible applications of spin-orbit phenomena will be both pursued, in the linear and nonlinear regime, including materials such as liquid crystals, light-written nanogratings in glass, two-photon polymerized structures and biased nanoguides in Lithium Niobate.

  • Photocatalysis for the synthesis of fuels and sustainable resources
  • The world faces tremendous challenges in environmental technology, as the emission of greenhouse gases has to be reduced rapidly and significantly to achieve climate goals. One of the main unsolved problems is the lack of technology for energy storage. A promising approach is the conversion of exhaust gases (CH4, CO, CO2, H2) to storable and transportable resources. Catalytic processes are the method of choice for this purpose, but it is difficult to trigger these reactions with thermal activation energy only. The present project should investigate the control of chemical reactions to produce fuels and sustainable resources using innovative laser technologies. Among these, coherent control using few-cycle pulses and pulse shaping will be applied to drive chemical reactions in the desired direction.

  • Fs-laser induced cross-linking of corneal tissue
  • This highly interdisciplinary project is a collaboration with physicians and engineers of the universities in Göttingen and Jena to evaluate treatment scenarios using fs-laser induced cross-linking of corneal tissue. Possible applications are the treatment of keratoconus, or even refractive correction of myopia. Currently, the method of UV (A)-riboflavin crosslinking is used to stabilize the cornea in the keratoconus. Riboflavin is applied locally and cross-linked by UV (A) radiation. Yet, the precision of this procedure is low, and the exclusive treatment of diseased areas is not possible. In this project, fs-lasers should be used for the cross-linking of corneal collagen fibres. Using a high-speed scanner system, the focal spot of the fs-laser can be precisely controlled on the corneal surface allowing for a selective treatment of diseased areas.


    Prof. Gerhard Paulus (Jena)
  • Strong-field laser physics
  • A central goal of molecular physics is to steer the outcome of chemical reactions. Ultrashort laser pulses provide a powerful tool to study and also control molecular bonds on ultrashort time scales. However, the interaction of molecules with laser pulses is governed by the excitation of bound or unbound electronic states, while most conventional chemistry proceeds on the electronic ground state via excitation of vibrational levels. Using ultrashort IR lasers, we strive to investigate the largely unexplored field of ground-state photochemistry. To this end, we use highly sophisticated laser technology as well as an advanced ion beam apparatus with time- and position-resolved coincidence detection. Available topics range from instrumentation and laser technology to data analysis and theoretical simulations.

  • Nanoscale XUV imaging
  • XUV radiation has distinctive advantages for imaging, including resolution and element-specific contrast. We recently invented XUV coherence tomography (XCT), which enables non-destructive cross-sectional imaging with nanoscale resolution. Available topics include the combination with other lens-less imaging modalities, ultrafast nanoscale imaging, and multispectral imaging.

  • Precision X-ray polarimetry
  • We have developed X-ray polarimeters providing extinction ratios of better than 1E-10, by far the best in the world and also by far beyond of what is possible in the optical regime. The ultimate goal is to measure the birefringence of vacuum polarized by a strong laser – and we believe that we have sufficiently advanced X-ray polarimetry to do such an experiment at the European XFEL in the next years. However, precision X-ray polarimetry offers a large range of other research opportunities. One of these is X-ray polarization microscopy. Another, in collaboration with Professor Röhlsberger, X-ray quantum optics.

  • Tailored Light-induced molecular potentials
  • The structure and dynamics of a molecule are governed by the forces between its nuclei and electrons. These forces give rise to the molecular potentials, on which nuclear motion and chemical reactions occur. Intense femtosecond laser fields can exert external forces comparable to the intermolecular ones. Thus, they can be used to manipulate molecular potentials on the timescales on the time scale of the nuclear dynamics. In this project, we will explore such routes to manipulate chemical reactions by means of tailored laser light.


    Prof. Nina Rohringer (Hamburg)
  • Stochastic phase-space methods to treat time-dependent open many-body quantum systems in external laser fields
  • The advances in the fields of short-pulse laser and x-ray free-electron laser pulse creation allows probing of correlated and collective electron dynamics at its inherent attosecond timescale. State-of-the art methods to treat the interaction of ultrashort laser pulses with many-electron systems often resort to single-active electron approaches that are inherently unable to treat correlated many-body dynamics. On the other hand, computationally tractable time-dependent many-body theories, such as time-dependent density functional theory, the time-dependent Hartree Fock method, or time-dependent configuration interaction can account for electron correlation only to some limiting extent. This project focuses on the development of an alternative method to describe time-dependent many-body quantum systems. Recently, our group developed a theoretical framework that allows for a stochastic phase-space description of the time-dependent density matrix of an open many-body quantum system. In the project, the successful student should extend this formalism to treat correlated electron systems in external laser fields. Within this framework electron correlation beyond the Hartree-Fock level will be captured by stochastic processes defined by an appropriate noise correlation function, that has to be derived. Numerically, this will result in solving coupled stochastic differential equations, to sample the two-particle reduced electronic density matrix. We are looking for candidates with a strong interest in the development of novel theoretical methods, strong analytical skills and an interest in numerical implementation (programming).


    Dr. Vladislav Yakovlev (Munich)
  • Attosecond metrology
  • We study some of the fastest processes that accompany light-matter interaction. As our primary experimental approach, we investigate the light-controlled motion of charge carriers photoinjected within a time interval as short as a femtosecond. Combining our experimental and theoretical expertise, we develop novel methods for observing electron dynamics with attosecond temporal resolution. We also apply these methods to study processes that determine the fundamental speed limits of optoelectronics. For more information, see https://www.attoworld.de/atto-20.html

  • The coupling of physics and photonics for the development of new technologies, applicable for bio-medical sciences.
  • Leveraging the controlled electric field transients available at the Max Planck Institute of Quantum Optic, that push the limits of current laser technology, to achieve temporal confinement of the ionization of molecular systems, we aim for complete temporal separation between the excitation and the resulting radiation. We are investigating the effects of rapidly removing an electron from a molecule using an impulse-like intense laser field and studying the radiation emitted from the resulting molecular ion, within the IR, mid-IR and THz spectral ranges. This work should have impact within the fields of THz science, spectroscopy, and bio-medical sciences.


    Prof. Peter Hommelhoff (Erlangen)
  • Particle acceleration on a nanophotonic chip
  • Before particle acceleration comes transport. Transport through an accelerator structure means that a particle beam can be actively steered through the required elements needed to build a particle accelerator. This is what we have achieved through a nanophotonic channel (Nature 2021). Based on this, we are now ready to build the particle accelerator on a chip. Various topics have to be tackled for this, ranging from electron beam simulation driven with the optical nearfields, via structure optimization to the integration of the optics to power the structure.
    * Building the accelerator on a naonphotonic chip
    * Next to acceleration, these structures also allow generation of attosecond electron bunches, which we will use for various laser pump--electron probe experiments.


    Prof. Franz Kärtner (Hamburg)
  • Efficient THz generation
  • We explore different ways to overcome the Manley-Rowe limit for THz generation with lasers through optical rectification through cascading in periodically poled nonlinear materials. Students will get familiar with the use of high energy short pulse lasers in driving strongly nonlinear processes. Eventually conversion beyond several percent from optical to THz is realized. The high energy THz pulses are used ifor THz acceleration.


    Prof. Stefan Karsch (Munich)
  • Development of ultralow-emittance electron beams for driving high-brilliance X-ray sources

  • Prof. Nicolas Joly (Erlangen)
  • Photonic crystal fibres under pressure, one, two, three photons sources for quantum optics

  • Prof. Peter Loosen (Aachen)

  • Systems integration and realization of high-power digital laser beam shaping
  • The use of process-adapted intensity distributions and the design of optical systems for the realization of these intensity distributions is essential for digital photonics production. We are investigating new ways to generate flexible and highly dynamic intensity profiles. With the help of so-called Spatial Light Modulators (SLMs), among other devices, the phase front of the laser radiation can be manipulated digitally with high resolution which enables the dynamic control of the intensity distribution in the processing plane. Commercially available SLMs are already capable of shaping the phase front of a laser beam. However, there are significant limitations to this. For example, neighboring pixels influence each other in their phase deviation (crosstalk). For the efficient use of SLMs, a method has to be developed to circumvent, compensate or at least take into account the existing limitations in phase matching. In this project, optical systems with integrated SLMs will be developed and validated for selected applications in laser material processing.


  • Application adapted intensity distributions
  • In laser materials processing, the intensity distribution of the laser beam significantly influences the temperature profile that is induced in the workpiece. As this temperature profile on the other hand accounts for the obtained material modifications, the processing quality and efficiency can be influenced by adapting the intensity distribution to the respective process. However, the computation of such an application adapted intensity distribution is not straightforward as an inverse heat conduction problem must be solved. In our group, we develop numerical solution methods which combine FEM and FDM solutions of the heat conduction equation with state-of-the-art optimization strategies. Up to date, these methods have been applied to laser heat treatment. In the research project, the algorithms will be extended to more complex materials, geometries, and especially processes such as laser powder bed fusion, laser welding or laser structuring with ultra-short pulsed radiation.


  • Digitalization and digital twins in optical technologies
  • The increasing digitization of products and production processes not only changes our everyday life and creates new possibilities almost daily, but also impacts the design process and operation of optical systems. The use of sensor technology during assembly (wavefront sensor) and the integration of miniaturized sensor technology in optical systems enables the feedback of the acquired data into the digital (optical) models. It becomes possible to create a digital optical twin (DOT), which accompanies an optical system over its entire life cycle. This makes it possible to generate service life forecasts, enable targeted adjustments and plan adapted maintenance intervals at an early stage. In addition, improvements for future product design upgrades can be derived from the obtained data. Another research topic in the context of digitization is the use of artificial intelligence and the exploration of quantum computing for optics design and multi-physics optimization problems. One aim of using AI algorithms is the acceleration and automation of the design process of optical systems. Currently, the use of reinforcement learning to automate the design process of optical systems is being investigated.


    Prof. Heinrich Schleifenbaum (Aachen)
  • Interaction of laser radiation and polymers in Laser Sintering
  • Laser Sintering (LS) is a powder bed based Additive Manufacturing (AM) technology for the processing of polymer powders. To generate polymer parts with LS, CO2 lasers with a wavelength of 10.6 µm are used as standard, as the CO2 laser radiation is strongly absorbed by the polymer powders. In contrast, polymers hardly absorb any radiation in the near infrared (IR) at about 1 µm wavelength (e.g. fiber and diode laser radiation). In order to deepen research in this field, a fundamental understanding of the interaction of the laser radiation with different wavelengths and polymer materials must be developed. For this purpose, both the material itself as well as the interaction with the laser source have to be fundamentally investigated. Material combinations of polymers and absorber materials increase the absorption capacity at wavelengths of approximately 1 µm and offer the possibility to process polymers, but at the same time affect the resulting component properties. In addition, the fragile heat balance in LS (maximum variations of ±2-4°C) is to be analyzed with improved heating concepts in order to extend the knowledge gained on the processing of e.g. high-performance polymers such as PEEK with different radiation sources.

  • Simulation of the correlation between laser radiation and the polymer melting process in Laser Sintering
  • Nowadays, laser technology is used in many cases to melt materials. Especially in the field of Additive Manufacturing (AM) this is one of the most common processes (e.g. in Laser Sintering – LS). However, the exact interaction between the laser radiation and the molten material particles is not yet well understood. In view of the research into the processing of polymers by LS using laser beam sources with wavelengths that are insufficiently absorbed by the polymers, the sintering process must be analyzed in detail. The wavelength absorption as well as the conversion of the introduced energy to form sintered and molten polymer particles have not been sufficiently investigated so far. As a result, the formation of the molten material in correlation with the laser radiation, the formation of macro- and microscopic defects and the thermal behavior in x-, y- and z-direction must be studied. Therefore, different simulation methods (e.g. DEM, FEM) and monitoring equipment (e.g. pyrometers) will be further developed and applied to gain a fundamental understanding of the interaction between laser radiation and melting behavior, which will be calibrated and validated by iterative experiments.

  • Adaption of the chemical material composition for cross-layer crystallization in Laser Sintering
  • Laser sintering (LS) is a powder bed based additive manufacturing (AM) technology for the processing of polymers. Since LS is a layer-by-layer process in which the material is sintered and melted, the interconnection between the individual layers is of utmost importance to achieve the required stability of the component in the build-up direction. This could be achieved by increased crystallization of the material across the layers, requiring research into the adaption of the chemical composition of the polymer. Furthermore, to produce high-performance polymer components with LS, additives such as carbon or glass fibers are often added to the base material itself. During the melting process of the layers to each other, these fibers are interference bodies and reduce the layer bonding. Accordingly, the matrix material (base polymer) must achieve the required crystallization across the layers and therefore requires material adaptation which has to be investigated.


    Prof. Henry Chapman (Hamburg)
  • Lensless Imaging using Coherent Electrons
  • The methods of coherent diffractive imaging and ptychography replace a lens with an algorithm to obtain quantitative phase-sensitive images, and may provide advantages over conventional electron microscopy of macromolecules. This project will develop simulations of coherent electron diffraction under realistic conditions and compare with experiments, and investigate new algorithms to recover images from the diffraction data. We are looking for a candidate with a strong interest in imaging and Fourier optics, and who is capable of programming and performing data visualisation.

  • High resolution X-ray holography
  • One aspect of in-line holography is that the reference wave greatly amplifies the weak scattered wave from a small object such as a virus. With revolutionary new X-ray optics it becomes possible to record highly magnified in-line holograms of nanometer-sized objects. This project will explore the potentials of this for imaging biological materials, investigate the dose requirements, and experimentally demonstrate 3D imaging. The successful candidate should have a strong background in optics and imaging, and strong programming skills.

  • Time-resolved serial crystallography
  • This project will extend the method of serial femtosecond crystallography using X-ray free-electron lasers and synchrotron radiation facilities to investigate the dynamics of proteins induced by novel triggers, such as terahertz radiation or photo-acoustic waves. The candidate will have a unique opportunity to work on forefront research at advanced X-ray facilities as well as develop and test new experimental methods in the laboratory. The project combines experimental physics, structural biology, and computational analysis. We are therefore searching for a candidate with a strong interest in multidisciplinary research.


    Prof. Stefan Karsch (Munich)
  • Development of ultralow-emittance electron beams for driving high-brilliance X-ray sources

  • Prof. Matthias Kling (Munich)
  • Attosecond imaging and spectroscopy of light-induced dynamics in molecules and nanostructures
  • We are interested in ultrafast correlated and collective electron dynamics that unfold when complex materials are exposed to intense, ultrashort laser fields. In particular this includes the attosecond control and tracing of strongly coupled electron-nuclear dynamics in quantum systems such as molecules, and of collective electron dynamics in nanostructured materials, and lightwave-driven petahertz (nano)electronics. We develop and use multi-dimensional imaging techniques in conjunction with (attosecond) pump-probe experiments to gain detailed insight into the dynamics from the interaction of these materials with near-single cycle laser fields of typically attosecond to femtosecond duration. We actively push the theoretical modeling of the rather complex multi-charge dynamics, which are partly carried out in our group using Monte-Carlo simulations with more intricate models within collaborations.


    Prof. Nina Rohringer (Hamburg)
  • X-ray diffraction from population-inverted atoms: opportunities for single-particle imaging
  • X-rays provide a unique opportunity to obtain the structure of matter at atomic resolution. In crystals (periodic arrangement of atomic or molecular constituents) x-ray diffraction is successfully used over more than 100 years to unravel the atomic and electronic structure with applications ranging from simple materials to large biological complexes. Despite the advent of novel, ultrabright x-ray sources -- x-ray free-electron lasers (XFELs) -- the study of single particles of biological interest remains challenging. The challenge manifests itself in the inherently small elastic x-ray scattering strength (giving rise to diffraction) combined with strong competing processes such as ionization and/or Compton scattering. In this project, we will develop a novel imaging technique, relying on two-color pulses of XFELs: The first x-ray pulse will prepare atoms of the sample in core-excited states by promoting an electron of the inner-most electronic shell into a valence shell. The second x-ray pulse, tuned to an inner-shell transition (for example K- transition), will elastically scatter on a set of atoms in states of population inversion. Two effects will enhance the scattering signal: On resonance, anomalous x-ray scattering gives an enhancement of the scattering strength. Moreover, scattering on core-inverted atoms can result in stimulated emission, that eventually gives rise to an exponentially enhanced signal amplification. The signal from population-inverted atoms can be analyzed together with non-resonant scattering from other atoms of the object, thus enhancing the contrast. The successful candidate will develop the concept and theory of the novel approach and in the later stage of the project, will participate in proof-of-concept experiments at XFEL sources.

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