Pre-Pulse Contrast Enhancement at PHELIX via Millijoule-Level Ultrafast Optical Parametric Amplification

A high temporal contrast on the nano- and picosecond time scales has become a critical laser parameter since the development of CPA-based laser systems. Even today, with the latest generation of petawatt-class lasers, which can reach peak intensities of up to 10$^{23}$ W/cm² in the focal plane, this intensity-increasing trend continues, and the control and enhancement of the temporal contrast have gained more significance than ever before. Although there are experimental schemes that may exploit an imperfect temporal contrast to their benefit, the ultimate goal still remains to produce an absolutely clean temporal pulse that can be manipulated as desired. To achieve this, every contrast-degrading feature, such as amplified spontaneous emission (ASE), pre-pulses, and the CPA-specific ps-pedestal, must be either cleaned or completely avoided.

While PHELIX already provides an ASE contrast of up to 12 orders of magnitude, it is still plagued by the ps-pedestal and numerous pre-pulses that pre-dominantly originate from a high-gain regenerative amplifier in the front end. In an effort to improve the pre-pulse contrast, a high-contrast, millijoule-level ultrafast optical parametric amplifier was developed to completely avoid said front-end amplifier. By this, several pre-pulses have been eliminated from the system and a pre-pulse-contrast enhancement of almost three orders of magnitude to a contrast of 6.2 ⋅ 10$^{-11}$ was achieved.

In this talk, I will report on the development of the high-contrast, ultrafast optical parametric amplifier as the first amplification stage for the PHELIX facility in Darmstadt and the PENELOPE facility in Dresden, and detail the results that followed the implementation at PHELIX.