Röder, Simon (2024)
Optical Control of the Temporal Contrast in Chirpe-Pulse-Amplification Lasers.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00028149
Dissertation, Erstveröffentlichung, Verlagsversion

Kurzbeschreibung (Abstract)

This work aims to develop novel techniques for purely optical control of the rising edge in the temporal profile ultra-intense laser pulses. The purpose of this is to facilitate research with controlled preplasma conditions at highest intensities. The approach pursued in this work for this purpose consists of exploiting the dependency between the beam size in the pulse stretcher and the shape of the rising edge. Over the course of this thesis, I have developed an analytical model that is capable of describing the formation of a rising edge in the stretcher of a chirped-pulse-amplification laser system. For the validation of this model in the frame of an experimental campaign, I have developed a corresponding stretcher setup. During this campaign, I experimentally validated the dependency of the slope of the rising edge on the beam size. Furthermore, I have validated that spatial apertures in the beam path to the stretcher condition the rising edge, as well as damages on optical surfaces in the Fourier plane in the stretcher. Subsequent to the experimental validation, I adapted the unfolded configuration of the developed stretcher to the requirements in the beam path of a chirped-pulse-amplification system. This unfolded setup omits optical elements in the Fourier plane, which, in agreement with the analytical model, causes an improvement of the rising edge. The setup further employs beam expansion for further improvement of the contrast due to the conditioning of the rising edge by the beam size. This novel, purely optical method for temporal-contrast manipulation was demonstrated in this work for the first time. By implementing the developed stretcher design at the Petawatt Hoch-Energie Laser für SchwerIoneneXperimente (PHELIX), I was able to improve the rising edge to a degree where it decreases below a contrast level of 5.7 · 10−10 within 30 ps prior to the main pulse, in comparison to previously around 100 ps. Hydrodynamic simulations of the interaction of this rising edge with an 100nm thick polystyrene foil yield that the achieved rising edge improvement corresponds to a reduction of the preplasma scale length by almost a factor of three. I published the results of this work in the journal "High Power Laser Science and Engineering".

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