Sprecher
Beschreibung
High power laser systems driving relativistic plasmas have applications in the generation of high energy, short duration particle and photon secondary sources. These mechanisms are typically extremely sensitive to laser contrast - pre-pulses and amplified spontaneous emission (ASE) that can trigger an expanding plasma long before the peak intensity is reached. As we enter the multi-petawatt regime, the requirements on laser contrast will become more stringent as peak intensity rises.
One commonly used method of improving a laser’s contrast is using plasma mirrors. These optical systems take advantage of the fast switch on time of an initially transparent medium as it is turned to plasma by the intense laser pulse itself. This has the effect that any light impinging before the peak of the pulse will not be reflected and is removed prior to the main interaction. Using a chain of two such optics, Double Plasma Mirror (DPM) systems have been effectively demonstrated to improve the contrast of laser pulses by 4-5 orders of magnitude, well before the rising edge at a few picoseconds before the peak of the pulse [1,2]. However, the impact very close to the peak as the intensity rises rapidly is less clear despite these timescales still being very impactful on the final plasma conditions.
Surface high harmonic generation (SHHG) from overdense plasmas is one application of high-power lasers that is extremely sensitive to laser pulse contrast [3]. Not only is SHHG a powerful source of extreme ultraviolet (XUV) and attosecond duration radiation, but it can also provide an effective benchmark of laser pulse contrast. Here we present characterisations of a DPM system currently in operation on the Gemini laser and its impact on the observed SHHG signal when a controlled pre-pulse is added. Furthermore, we discuss planned developments on the JETI-200 laser and the expected performance for SHHG experiments.
[1] A. Lévy et al., “Double plasma mirror for ultrahigh temporal contrast ultraintense laser pulses,” Optics Letters, vol. 32, no. 3, p. 310, Jan. 2007, doi: https://doi.org/10.1364/ol.32.000310.
[2] I. W. Choi et al., “Highly efficient double plasma mirror producing ultrahigh-contrast multi-petawatt laser pulses,” Optics Letters, vol. 45, no. 23, pp. 6342–6342, Oct. 2020, doi: https://doi.org/10.1364/ol.409749.
[3] S. Kahaly et al., “Direct Observation of Density-Gradient Effects in Harmonic Generation from Plasma Mirrors,” Physical review letters, vol. 110, no. 17, Apr. 2013, doi: https://doi.org/10.1103/physrevlett.110.175001
