The general goal of this project is the development of sophisticated short pulse laser sources. Laser concepts based on Ti:sapphire, rare-earth-doped crystals and semiconductors for femtosecond and picosecond oscillator and amplifier systems are under investigation. One focus of this project is the progress of compact diode-pumped femtosecond laser systems. The potential of novel ytterbium-doped active materials and semiconductor structures is studied in the 1-µm spectral range. Optically-pumped semiconductor disk lasers (SDL) have gained much attention in recent years, including the possibility to achieve mode-locking by the use of a semiconductor saturable absorber mirror (SESAM). This all-semiconductor approach is particularly interesting because of its simple mode-locked laser design – see feature article. Yb-doped laser crystals are well-suited for building conceptually simple and highly efficient diode-pumped sub-100 femtosecond lasers. Single-walled carbon-nanotube saturable absorbers (SWCNT-SA) are unique nanostructures which exhibit, beside novel electrical, chemical, and mechanical, also interesting optical properties. Optical features such as fast third order optical nonlinearity and saturable absorption qualify them as a potential replacement for semiconductor-based ultrafast saturable absorbers (SESAMs). Furthermore, SESAMs have to be fabricated by very complex epitaxial processes and additional treatment is often required for reducing the recovery time of the absorbing layer. Passive mode-locking with transmission- and reflection-type SWCNT-SA is demonstrated for Yb-doped bulk laser media.

A major part of the project is dedicated to the development and the optimization of special UV lasers, that are required for the operation of RF photo injectors at the FLASH FEL (DESY Hamburg), PITZ (DESY Zeuthen) und the forthcoming XFEL. Within 2008, this part of the project was mainly focused on the development of a new pulse-shaping technique optimized for photo injector drive lasers.

Another part of the project is directed towards improvement of Ti:sapphire laser technology, especially applied to the multi-terawatt High Field Ti:sapphire Laser (HFL). This concerns increasing the peak power through improvement of the pulse shape, recompression and increasing the energy available for interaction experiments, improvement of temporal contrast related to amplified spontaneous emission to the value sufficient for pre-pulse free laser-matter interaction (contrast >10¹⁰, for peak intensity I >10²⁰ W/cm², increasing the stability of HFL laser operation and other associated issues.

Furthermore, the development of a laser driver for an x-ray lasers (XRL) based on the thin disk laser technology is part of the project. Using Yb:YAG as active material, the laser system is planned to deliver pulses up to 1 J at 100 Hz repetition rate. The specific optical arrangement based of chirped pulse amplifications (CPA) allows to generate optional nanosecond- or bandwidth-limited picosecond- pulses. Although the laser system is optimized for XRL pumping it might be an interesting choice as a pump source for an OPCPA (optical parametric chirped pulse amplification) laser system generating femtosecond pulses with a very high contrast in the 100 mJ range.