In order to extend the parameter range of our primary laser sources we undertake intensive development on secondary sources concentrating on two main directions:

Pulse compression

The institute has a considerable expertise in high power pulse compression using hollow-core fibers: besides the conventional rigid capillaries, we also develop the stretched flexible hollow fiber technology, which is particularly suited for multi-mJ operation thanks to the free geometrical scalability of this kind of waveguides. Furthermore, we apply Kagome hollow-core photonic crystal fibers and multi-plate continuum generation in our high repetition-rate systems. The performance of a novel technique based on multi-pass cells is currently investigated. The various techniques are utilized for post-compression of our OPCPA systems. Further high power pulse compression activities include the compression of multi-mJ pulses from TW-level Ti:sapphire amplifiers in stretched flexible hollow fibers as well as efforts to compress high-energy few-picosecond pulses from laser systems based on Yb-, Ho- and Cr-doped materials.

Nonlinear frequency conversion

Nonlinear frequency conversion techniques are used for the generation of intense light fields beyond the wavelengths that can be addressed by primary sources, i.e., spanning the entire wavelength regime from the THz to the XUV and X-ray domain. On the long wavelength side, we target the generation of single-cycle THz fields with field strengths of up to 10 MV/cm and beyond for use in a wide range of experiments addressing field-driven processes on attosecond to femtosecond time scales. At the other end of the wavelength spectrum, we undertake efforts to optimize the generation of soft X-rays in the water window and beyond using HHG. The past few years have revealed a number of surprising results in HHG research, in particular at high laser intensities, high target pressures and/or multi-jet geometries, suggesting that the process is not yet fully understood and that the potential for efficient XUV/soft X-ray generation is not yet fully realized. Moreover, the dynamics underlying the generation process in multi-color fields with tailored polarization states is not yet fully explored, which places them in the focus of our research.