Nonlinear Optics
Prof. Dr. Gerhard PAULUS
Laser lab setup.
Image: Jan-Peter Kasper (University of Jena)
Prof. Dr. Gerhard Paulus
Image: Jan-Peter Kasper (University of Jena)Prof. Dr. Gerhard G. PAULUS
Email: gerhard.paulus@uni-jena.de
Phone: +49 3641-9-47200
Prof. Paulus holds the Chair of Nonlinear Optics and is Director of the Institute of Optics and Quantum Electronics at Friedrich Schiller University Jena. He is also a member of the Directorate of the Helmholtz Institute Jena.
Research Areas
The research of Prof. Paulus focuses on strong-field and attosecond laser physics, nanoscale imaging with extreme-ultraviolet radiation, and high-precision X-ray optics. Research topics include:
- Strong-field ionization and electron dynamics
- Attosecond and few-cycle laser physics
- Electron and molecular dynamics in intense laser fields
- High-harmonic generation
- Nanoscale XUV coherence tomography
- XUV and X-ray imaging
- High-precision X-ray polarimetry
- Strong-field QED
Teaching Fields
- Introductory physics
- Fundamentals of modern optics
- Nonlinear optics
- Strong-field and attosecond laser physics
- X-ray physics and free-electron lasers
- Renewable energies
Research Methods
The group combines ultrafast laser techniques with electron, XUV and X-ray spectroscopy and imaging. Core methods include:
- Photoelectron and momentum spectroscopy
- Few-cycle and carrier-envelope-phase controlled laser pulses
- High-harmonic generation
- XUV spectroscopy and interferometry
- XUV coherence tomography
- X-ray polarimetry
- Coincidence spectroscopy
- Vortex and structured laser beams
Prof. Gerhard Paulus with this team.
Image: Jan-Peter Kasper (University of Jena)Recent Research Results
Current research combines strong-field and attosecond physics with the development of advanced table-top XUV and soft-X-ray sources for spectroscopy and nanoscale imaging. In strong-field physics, recent work has used laser-induced electron diffraction to probe coupled continuum and valence-electron dynamics in xenon [1]. The experiments reveal how a recolliding electron wave packet can encode ultrafast changes in the ionic core, providing access to electronic dynamics on sub-femtosecond time scales.
A second focus is nonlinear spectroscopy in the extreme ultraviolet. Using a high-flux high-harmonic source around 26.5 eV, the group demonstrated coincidence measurements of two-photon double ionization of argon and identified a pronounced contribution from an autoionizing resonance [2]. The underlying source delivers coherent quasi-monochromatic XUV radiation with photon fluxes around 10¹³ photons per second and enables ion-electron coincidence as well as pump-probe spectroscopy in a compact laboratory setting [3].
Another major research direction is XUV and soft-X-ray coherence tomography. The method provides non-destructive cross-sectional imaging of buried nanostructures by exploiting the broad spectral bandwidth and short wavelength of high-harmonic radiation. Recent work extended the approach into the soft-X-ray water window and demonstrated depth-resolved imaging with an axial resolution of about 12 nm, even for weakly reflecting and comparatively rough samples [4]. This substantially broadens the range of materials and structures accessible to laboratory-based coherence tomography.
Complementary work on coherent XUV imaging aims at wavelength-scale spatial resolution using lensless techniques such as coherent diffractive imaging, Fourier-transform holography and ptychography [5]. High-precision X-ray polarimetry and tests of quantum electrodynamics in extreme fields remain further important activities of the group [6,7].
[1] Liu et al., Phys. Rev. A 110, 013118 (2024).
[2] Hell et al., Phys. Rev. Research 7, L032030 (2025).
[3] Späthe et al., Rev. Sci. Instrum. 96, 123009 (2025).
[4] Reinhard et al., Light Sci. Appl. 15, 79 (2026).
[5] Eschen et al., APL Photonics 10 (2025).
[6] Loetzsch et al., Nature 625, 673 (2024).
[7] Marx-Glowna et al., J. Synchrotron Radiat. (2026).