Our group focuses on the generation of novel particle and photon beams (the latter in close collaboration with F. Grüner) from laser driven sources. This on one hand involves the study and control of ultrahigh-intensity laser interaction with plasmas, on the other hand drives the improvement of the drive laser pulse parameters through continuous laser development.
In order to ensure competitiveness of our research in plasma physics, we continue to improve our main tools, the driving laser pulses. Not only a constant increase in the achievable output power qualifies a long-term-successful laser infrastructure, but also the constant improvement of not-so-obvious laser pulse parameters such as temporal contrast, focusability, shot-to-shot repeatability and availability for user experiments.
a) ATLAS-100 high-power Ti:sapphire laser
The ATLAS-100 Ti:sapphire laser delivers 25 fs, 2J pulses (80 TW) with 5 Hz repetition rate. Its frontend incorporates a modified commercially available regenerative amplifier with active spectral shaping, allowing to optimize the pulse bandwidth through the whole amplification process, while keeping prepulses and ASE pedestals at a very low level. Beam smoothing and adaptive optics ensure close-to-optimum spatial coherence of the output beam, and a new plasma mirror setup is installed to further improve the temporal contrast.
b) Petawatt Field Synthesizer (PFS)
The development of the PFS is an attempt to overcome the limits of conventional laser technology with regard to shortest pulse duration, high repetition rate, peak power and temporal contrast. We rely on the technique of optical parametric chirped-pulse amplification with the added benefit of pumping the amplifiers with high-intensity, few-ps pump pulses. This strategy allows the use of very short amplifier crystals leading to an intrinsically broader phase-matching bandwidth, a shorter time-window for contrast-reducing parametric fluorescence, and no heat load (= no distortions) in the main amplifiers. The achievable pulse durations should be on the order of 5 fs, ensuring PW-scale peak powers at moderate pulse energy. While this strategy for the laser amplifiers seems to solve a lot of problems at the same time, the main system risk is the necessary high-repetition rate, ps, high-energy pump laser. Its development focuses on diode pumping technology and Yb-doped laser materials.