Below you can find the available PhD Research Topics for application into the second phase of the program (PhD research). When applying via the application portal, you are free to choose up to five topics. If you are interested in the Fellows’ research activities, visit our Fellows page and click on the institutions of interest to get to the relevant website. Unfortunately, it is not possible to apply for a PhD Research Topic with a Fellow, if he/she is not listed here with a topic. However, during the application procedure there is the option to make fine adjustments on topics.

X-ray free-electron lasers provide spatially coherent X-ray pulses that can be used to record noisy diffraction patterns of single molecules, molecular complexes, and virus particles. Iterative algorithms can be used to combine and phase the patterns to directly synthesise an image. In this project, such single-molecule diffraction will be obtained from molecules oriented with respect to each other in disordered crystals, and algorithms developed to not only phase the patterns but recover conformational variability of the molecules. The project will also investigate the feasibility of inducing disorder in molecular crystals to gain structural information. Experiments will be conducted at facilities such as the European XFEL and PETRA III in Hamburg or the Linac Coherent Light Source in California.
Development of quantum technologies dictates a need for scalable sources of highly entangled photon pairs. This PhD project is aimed at engineering a source based on parametric down-conversion in a nanometer-size strongly nonlinear layer. The phase matching in this source will be sacrificed to obtaining ultrabroad spectrum, ultrafast correlations, and a very high degree of spectral and spatial entanglement.

Two-dimensional semiconductors are the first class of atomic layer materials with a high degree of optical activity. Due to their unusual geometry, they exhibit extremely strong and highly unexpected light-matter interaction. In comparison to bulk semiconductors they have superior linear and nonlinear coefficients, extended excitonic lifetimes, spin-valley coupling and fluorescence. They are a highly attractive platform for fundamental experiments related to effects induced by dimensionality and also suitable for applications, e.g. sources for entangle photon pairs and novel imaging modalities.

My group does specialize on integrating two-dimensional semiconductors with optically resonant structures such as monolithic and optical fiber based cavities to further enhance and tailor their interaction with light. This project shall focus on both fundamental effects, which take place in resonantly enhanced two-materials, such as emission enhancement and photon statistics, as well as on the exploration of possible applications for sensing, imaging and the generation of non-classical and entangled states of light.

New concepts have brought about a paradigm shift in the physical limits to optical analysis of molecular systems. Imaging resolutions of a few nanometers have been demonstrated, well beyond the Abbe/Rayleigh limits. The recently demonstrated MINFLUX concept (Science 355, 606-612 (2017)) outlines a path to further improved minimally invasive, low-light-level analysis, in principle down to Ångström length scales. This will open up entirely new experimental opportunities in the study of macromolecules and beyond.

The successful candidate(s) will develop physical measurement schemes based on MINFLUX and related concepts to analyze molecular systems at highest resolution. Candidates should be highly motivated and prepared to work within a truly multidisciplinary team. They should have (or expect to complete soon) a Masters or equivalent degree in Physics or Physical Chemistry or a comparable qualification. A willingness to master challenges in optical design, computer-driven experimental control and data analysis and, crucially, in-depth study of a problem by critical thinking and dedicated physical simulation are all central to success.

Rare earth ions doped into crystalline solids can show exceptional optical and hyperfine coherence, which makes them promising candidates for quantum optical applications ranging from quantum memories to quantum computing and sensing. The project will expand our activity on the efficient optical detection and quantum control of individual ions to realize optically addressable qubit registers, using fiber-based microcavities to enhance optical transitions and high-resolution spectroscopy for selective addressing of ions.
Photonic crystal fibre (PCF) consists of air-channels surrounding the central core region. By properly adjusting the size of the holes and their respective separation it is possible to engineer the dispersion landscape as well as the nonlinearity. These parameters are essential to achieve very large spectral broadening of the input beam. Although these ultra-broad spectral sources are nowadays routinely used for many applications, they also suffer from input noise, which can yield fast change of the generated supercontinuum (SC) at the shot-to-shot level. Another important feature is the polarisation of the generated light. In general, the polarisation across the whole SC is not fixed and this can strongly hamper many applications. Recently it was shown that twisting the PCF, either during the fabrication process or by post-processing it, results in circular birefringence, hence preserving guided circularly polarised light. In this project, we plan to explore the properties of such a twisted fibre in the nonlinear regime, aiming at the generation of SC with a well-defined polarization state.
Relativistic Thomson backscattering of laser pulses from laser-driven ultrashort electron bunches is a promising method for realizing high-brilliance, fs-X-ray sources with photon energies ranging from 15 keV to multiple MeV. Such sources have first been developed in recent years, and so far the emitted X-rays have a bandwidth on the order of 10-20%. Significantly reducing this spread, which is a consequence of the high intensity of the scattering laser pulses needed for achieving a high photon flux is the first goal of this project. Therefore, the scattering laser pulses have to be chirped and spectrally controlled to lock the X-ray emission to one well-defined energy. After this has been achieved, multiple, energy- and delay- tunable electron pulses can be provided from the laser accelerator in order to generate synchronized multi-color X-ray pulses. Such a source will enable time-resolved X-ray-pump/X-ray probe spectroscopy on a variety of material samples or biological specimen.
Such strong fields lead directly to the production of sub-femtosecond electron bunches over short distances via velocity bunching. We are constructing a THz accelerator using laser generated THz radiation of high energy laser pulses as well as Gyrotrons. The accelerator is used for a free-electron laser like X-ray source. The potential candidates learn how to design, simulate and/or build THz sources, electron guns and accelerators as well as X-ray sources based on them. He/she will learn ultrafast lasers, nonlinear optics, accelerator physics, electron, optical and THz beam diagnostics and the physics of Free-Electron lasers. An advanced finite element based solver can be used for designing different electromagnetic components and processes. The ideal PhD candidates will work experimental and/or theoretical and get familiar with the simulation methods and the code and may further develop existing tools.We seek candidates with either a strong experimental and/or theoretical background/experience in one or more of the following fields ultrafast optics, accelerator physics, diagnostics, high-vacuum technology, electromagnetic theory, programming/ numerical skills (Matlab, C++, LabView) or high performance computing with C++, OpenMP, MPI and GPU programming are highly advantageous. The successful candidate should be self-motivated and will work in a team supported by a Synergy Grant of the European Research Council on cutting-edge topics at the intersection of ultrafast optics, accelerator physics and radiation sources. The research is performed in an international collaborations involving MIT and Stanford University.
We offer PhD opportunities in attosecond imaging and spectroscopy with complex molecules and nanostructures. The main focus of the research lies on elucidating light-induced correlated and collective dynamics in complex molecules, molecule-nanoparticle heterostructures, and nanostructures in experiment and theory, supported by international collaborations. For more details, see
Photonic integration allows the combination of hundreds of high-performance devices on a millimeter-size chip. Silicon photonics is a particularly attractive platform, enabling large-scale integration of photonic along with electronic components by exploiting highly developed fabrication processes from the field of microelectronics. Our group is currently exploring signal-processing concepts that exploit photonic integrated circuits and chip-scale frequency combs sources for ultra-fast processing of signals at THz bandwidths. To this end, we expand the capabilities of conventional photonic integrated circuits by harnessing the third dimension through advanced 3D nano-printing techniques. To reinforce our team, we are currently looking for an ambitious PhD candidate with strong theoretical and/or experimental background. Applicants should have completed a Master in Electrical Engineering, Photonics, Physics or related fields. We expect excellent writing and oral communication skills along with the ability to work independently.
Research projects include the synthesis of intense, controlled waveforms of laser light, the real-time observation and control of electron motion, exploring the ultimate limits of electronics and routes for approaching them, and the development of laser-based sources and techniques for early diagnostics and therapy of cancer.
Perovskite semiconductors form an interesting new class of optoelectronic materials. In addition to the impressive progressin the field of photovoltaics, these semiconductors also offer promising properties for light emitting diodes. When synthesized asnanocrystals, perovskite semiconductors can exhibit single photon emission. The thesis will focus on strategies to integrate these solution processable quantum emitters into more complex photonic circuits and devices. The work comprises the fabrication of such devicesusing digital printing techniques (ink-jet and aerosol-jet printing) and the spectroscopic characterization.
High-power fiber lasers have always been considered an average-power scalable laser concept. This impression has been sustained by the impressive exponential evolution of the output power of these systems over the last two decades. Thus, fiber systems are currently the laser technology that emits the highest average power with diffraction-limited beam quality. In this context it is easy to understand the shock that the fiber laser community underwent when a new thermally-induced non-linear effect, called transverse mode instabilities (TMI), was discovered in 2009. This effect is characterized by the sudden break-up and temporal fluctuations of the beam emitted by a fiber laser system once that a certain average power threshold has been reached. Consequently, TMI currently represent the strongest limitation for the further power scaling of fiber lasers and, thus, prevent new applications from being addressed.After several years of intense research, it became clear that the phenomenon of TMI arises through the convergence of optics, laser dynamics and temperature: the excitation of two or more transverse modes in the active fiber gives rise to a modal interference pattern that, in turn, inscribes a refractive index grating into the fiber core via the thermo-optical effect. This grating can potentially couple energy between the interfering modes. Once that the physics of the process are well understood, it is time to develop strategies to mitigate, or even exploit this effect… and it is in this frame where the Ph.D. thesis is set.This Ph.D. topic offers you the opportunity to explore a fascinating multi-physics phenomenon in the scope of high-power fiber lasers together with a group of scientists that are at the forefront of the research of TMI worldwide. The techniques that will be developed to mitigate or even turn TMI into a positive effect will have a wide-reaching impact. So, if you are a creative and curious mind, which wants to contribute to solving one of the most serious challenges of fiber laser technology, please do not hesitate in contacting us.
Carbon-based nanostructures and materials, such as graphene, carbon nanotubes and doped diamond crystals promising to revolutionize many areas of modern nanotechnology, including photonics, electronics and quantum computing. The presence and magnitude of lattice imperfections in such structures can have a crucial influence on performance characteristics of carbon-based devices, and, in some cases, define their functionality. Therefore methods of controlled creation and modification of such imperfection are actively studied worldwide. One novel idea is utilization for this purpose of short-wavelength radiation with energies in vicinity of carbon absorption K-edge at 280eV. Depending on the structure, the irradiation with photon of energies between 40 and 400eV have shown the potential for efficient targeted creation of such imperfections. This radiation in this energy region is known as extreme ultraviolet and soft X-ray radiation.The EUV-Technology group at RWTH Aachen University together with partners from Fraunhofer ILT and Research Centre Jülich is actively investigating interaction mechanisms of such radiation with matter. The group operates several high-intensity plasma-based sources of EUV radiation with tunable spectral characteristics and possibility to focus the radiation to sub-100µm spots. The candidate will have a unique opportunity to perform systematic irradiation studies on several material systems in order to determine the underlying defect creation mechanisms and critical parameters such as minimal required excitation energy and intensity. Defect type determination and analysis of its impact on the performance-relevant parameters of the structures will also belong to the responsibilities of the candidate. It is expected that the results of this study will have not only fundamental but also applied impact.
Quantum communication will enable the connection of quantum computer nodes and lead to long-termsecurity in encrypted messaging. Due to the fragile nature of quantum states long distance quantum communicationis not possible in optical fibres. A solution is quantum communication via satellites as most of the propagation is in outer spacewithout atmospheric absorption. We currently started several endeavours to realise satellite-based quantum key distribution.
Recent years have seen rapid progress in the new field of cavity optomechanics. By exploiting radiation forces interacting with mechanical vibrations, a whole range of applications are being explored, from ultrasensitive measurements to fundamental tests of quantum physics. In this research project, you will apply state-of-the-art tools of theoretical quantum optics and condensed matter physics to predict the behaviour of future systems comprising many mechanical and optical modes. These include optomechanical arrays where one may engineer topological transport, as well as unconventional setups, like levitated superfluid droplets.
Fluorescence imaging is a powerful technique to study biomolecular interactions in living systems at the highest possible temporal and spatial resolution. Within this PhD topic, STED nanoscopy-based instrumentation will be advanced through implementation of ultrafast scanners and adaptive optics. Moreover, novel data analysis tools based on single particle tracking and spatial/temporal correlations of pixel intensities will be further developed. These tools will be employed for a range of biophysical experiments on living systems (cells, tissues organisms) in our multidisciplinary group.
Quantum information science addresses various fundamental questions on how to harness quantum mechanical phenomena for processing and transmitting information. Photons are one highly promising implementation scheme for such systems. However, such photonic quantum architectures typically require very complex and sensitive settings when bulk optics are used. Within this project, quantum optical circuits will be implemented in a photonic chip based on integrated optical waveguides. Ultrashort laser pulses will pave the way for the direct inscription of 3D waveguide arrangements in a glass substrate building the quantum circuits. Photons serving as qubits can be manipulated by artificially implemented birefringent structures to change their state. One focus will be on realizing electronically reconfigurable quantum gates, which can be dynamically adapted by embedding liquid crystals into the chip. The project includes the design of the quantum chips, fundamentals of the fs-writing process, implementation of the quantum gates as well as the demonstration and evaluation of their functionality.
The project aims at investigating the dynamics of the ionization-induced fragmentation of such molecules with sub-cycle, i.e. attosecond resolution. To this end, the dependence of fragmentation on the carrier-envelope phase of few-cycle laser pulses is analyzed. Highly differential particle detection allowing the measurement of the momenta of all the fragments is employed. This is accomplished by a unique ion beam apparatus in which the molecular ions are generated, prepared, exposed to the laser radiation, and finally detected with spatial and temporal resolution in order to reconstruct their momenta. Their dependence on the carrier-envelope phase allows conclusions on the attosecond dynamics of the molecular ions in strong laser fields.
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.
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.
At the Chair for Laser Technology at the RWTH-Aachen University, in close collaboration with the according departments of Fraunhofer Institute for Lasertechnology, new lasers for special applications as well as laser-based manufacturing processes are developed. Cooperating with national, international, academic and industrial partners, main research topics include:


  • Ultrashort-pulse lasers
  • Lasers for air- and space borne applications
  • Tunable lasers
  • Compact EUV- and UV-sources for lithography and metrology

Laser Measurement Technology

  • Measurement in physical regime (e.g. dimensions and distances)
  • Measurement in chemical regime (e.g. Laser- Induced Breakdown Spectroscopy (LIBS), laser-induced fluorescence (LIF))
  • In-line measurement (e.g. production, recycling, laser-based manufacturing)

Laser-based Manufacturing

  • Laser cutting and –welding
  • Laser polishing and –structuring
  • Laser drilling
  • Medical technology and biophotonics

Digital Photonic Production

  • Process chains for laser-based production

Based on progressive research and development projects, many interesting and up-to-date research topics are available. Please contact us for latest information regarding open positions.

Based on progressive research and development projects, many interesting and up-to-date research topics are available. Please contact us for latest information regarding open positions.

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, or dielectrics, and explore applications thereof. Referential examples for such applications are, e.g., in the field of photon management in light harvesting or sensing devices. We have activities in the field of plasmonics, optical nanoantannas, metamaterials and metasurfaces, computational material design, and quantum optics at the nanoscale in place and are currently seeking a PhD student to reinforce our team.

Cooperative interactions of light with ensembles of identical atoms play an increasingly important role in optical sciences due to their relevance to quantum-optical coherent control schemes for quantum technology or metrology applications. A novel approach in this field is to move into the regime of hard x-rays and employ the ultranarrow resonances of Mössbauer nuclei to control the cooperative emission of x-ray photons. Mössbauer nuclei can be prepared as identical emitters in large numbers and very accurately positioned via micro- and nanostructuring techniques.The goal of this project is to explore new ways to control cooperative emission and radiative properties such as superradiance, subradiance, transparency, group velocity or spectral response by engineering position-dependent phase correlations between the identical x-ray emitters. This should be explored in this project via specially designed 2D and 3D nanostructures (waveguides, Bragg-gratings, Fresnel lenses) that contain Mössbauer nuclei and act as photonic structures for x-rays.This project is a joint initiative between the groups of Tim Salditt (Univ. Göttingen) and Ralf Röhlsberger (DESY, Hamburg). It is planned to perform most of these experiments at the PETRA III synchrotron and the European XFEL in Hamburg.
X-ray free-electron lasers (XFELs) are novel x-ray sources offering x-ray pulses of unprecedented intensities that open new opportunities to study correlated electron dynamics by nonlinear x-ray pump-probe techniques. The element specificity of x-rays, along with the short duration and extreme intensities of XFEL pulses enables nonlinear spectroscopic techniques, that will be a sensitive method for studying charge- and energy transport, coupled electron nuclear dynamics and reaction intermediates in catalytic processes, such as photosynthesis, nitrogen fixation and respiration. Metallic atoms play a crucial role in those processes, building the core of the chemical reaction centers. The project will focus on the theoretical description of stimulated electronic Raman scattering - one basic building block of nonlinear x-ray spectroscopy - in transition metal systems. Stimulated electronic Raman scattering launches electronic wave packets that can be subsequently probed by transient absorption spectroscopy. The project aims for quantitative predictive theoretical estimates of this process in transition metal model compounds, in particular the prediction of the nonlinear spectral output. The results will directly find application in experimental campaigns at XFELs (in particular the European XFEL) that will be conducted in close collaboration with experimentalists. The results will give insight into electron charge transfer processes in model systems that mimic systems of biological or chemical relevance.
Fluorescence-based nanoscopy methods, also known as “superresolution” microscopy, have substantially expanded our options to examine the distributions of molecules inside cells with nanometer-scale resolution and molecular specificity. In biophysical studies of aggregation-prone misfolded proteins and peptides, this has enabled the visualization of distinct populations of aggregated species such as fibrillar assemblies within intact neuronal cells, well below previous limits of sensitivity and resolution. Nanoscopy can facilitate detailed investigations of misfolded protein fate also in the context of the cell’s protein quality control systems and allow testing hypotheses of molecular mechanisms of cellular toxicity.The successful candidate will both innovate advanced optical nanoscopy approaches and apply them to help answer challenging and central questions in the pathobiology of neurodegeneration. He/she should hold (or expect to complete soon) a Masters or equivalent degree in Physics, Biophysics or Physical Chemistry, or a comparable qualification.
We have shown that x-ray radiation can propagated in highly curved waveguide channels and deflected tolarge angles. The goal of the thesis is to define advanced geometries of X-ray waveguides with beam splittersand couplers to generate and steer several coherent beamlets for advanced interference effects.

Selective Laser Sintering (SLS) is a powder bed-based Additive Manufacturing (AM) technology for the processing of polymers. When processing polymers powders using SLS, CO2 lasers with a wavelength of 10.6 μm are used as standard, since the CO2 laser radiation is strongly absorbed by the polymers. In contrast, polymers in the near infrared (IR) at approx. 1 μm wavelength (e.g. fiber and diode laser radiation) hardly absorb. Therefore, it is already common practice in the field of laser plastic welding to provide polymers with IR absorbers. In the field of SLS of polymers , however, no research work has been carried out to date on the use of alternative laser sources in combination with IR absorbers. In order to conduct more in-depth research in this field, a fundamental understanding of the interactions of laser radiation with different wavelengths and polymers must be carried out. Due to the insufficient absorbency of most polymers at short wavelengths of approx. 1 µm, different absorbers in different compositions are investigated with the polymers in the next step. The absorbers are used with the polymers in different proportions depending on the application and ensure that the mechanical properties are fulfilled.

  • Fundamental gain in knowledge of the interaction between laser radiation and polymers
  • Process development of the SLS with lasers of a wavelength of approx. 1 µm
  • New materials from a combination of absorbers and polymers to increase the absorbency at wavelengths of approx. 1 µm for additive greasing

Additionally, the heat balance for processing polymers by SLS needs to be as constant as possible (at least approx. ±2-4°C). Improved heating concepts by using other beam sources/shaping offer a great potential for processing high performance polymers (e.g. PEEK) and to improve the SLS process robustness.

Fiber optic sensors offer unique advantages for monitoring tasks especially in harsh environments and on large scale as they show e.g. immunity to electromagnetic interference, suitability for multiple parameter measurement and large multiplexing capacity. Optical time domain reflectometry or coherent and incoherent optical frequency domain reflectometry are enabling techniques for distributed sensing applications and thus for complex sensor networks. Optical fiber sensor networks depend more and more on the availability of advanced signal processing techniques based on e.g. model based signal processing, machine learning, digital twin modelling, etc.Within the proposed project fiber based sensor structures and advanced signal processing techniques will be investigated for application in distributed fiber optic multi parameter sensing networks. The project will be located at the institute of microwave and photonics where several projects in the context of fiber optic sensing and signal processing have been performed in cooperation with scientific and industrial partners in a well-equipped lab.Candidates should have very good basic knowledge in fiber optics, signal processing and interest in doing both, theoretical and experimental work.
Solar cells with novel absorber materials such as perovskites have the potential for higher conversion efficiency than traditional silicon-based solar cells—while even reducing manufacturing costs. However, inhomogeneities of the composition and phase as well as degradation issues have hampered the exploitation of the potential. Using hard X-rays from synchrotrons, we contribute to a better understanding of the growth and degradation processes by measuring their dynamics in real time under different conditions at high-resolution X-ray microscopes.
Quantum technology is a dynamic field in modern applied research in the field of laser physics. Two very fruitful branches are quantum communication via quantum key distribution (QKD) and quantum-enhanced imaging. Both fields rest upon photon-pair or multi-photon sources with very hard requirements on brightness, spectral range, and entanglement fidelity. Additionally, for useful practical application, such sources need to be ultra-stable, compact, and field-deployable.The task will be to work on the development and engineering of laser based sources of entangled photons with outstanding performance. In doing so, novel concepts besides spontaneous parametric down conversion (SPDC) in non-linear crystals should be followed and evaluated. Moreover, the sources shall be further harnessed to implement both novel QKD and quantum imaging schemes. For the challenge of miniaturization, this work will drive the replacement of macroscopic setups by photonic integrated circuits.
Together with experimentalists at the Laboratory for Attosecond Physics (LAP), we investigate new ways of inducing and controlling electron dynamics with light. Doing so, we theoretically explore new regimes of nonlinear light-matter interaction and clarify the fundamental speed limits of metrology and optoelectronic signal processing. Our primary goal is to develop theoretical descriptions and computational models for various processes that accompany the interaction of few- and subfemtosecond light pulses with solids. For our work, we use well-established general-purpose methods, such as the time-dependent density functional theory, as well as simplified models, where appropriate approximations allow us to gain deeper physical insight. Being a subgroup within the LAP, we participate in planning new experiments and supporting ongoing ones with theory.
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