Abstract
We report on an experimental study of the "coherent" contrast feature that frequently appears in petawatt(PW)-class laser pulses as an exponentially-rising pedestal within a few tens of picoseconds of the compressed pulse. We show that scattering from the diffraction gratings in the stretcher is the principal source of this feature. Replacing the gratings by new, higher-quality components resulted in an order-of-magnitude reduction in the intensity of the pedestal.
Highlights
In ultra-intense laser systems used for plasma physics research, contrast is one of the most important properties of the laser pulse
We have investigated the origin of the coherent contrast pedestal of a petawatt-class Titaniumsapphire laser system
Our results show that scatter from the diffraction gratings in the pulse stretcher is the main source of the coherent pedestal (CP)
Summary
In ultra-intense laser systems used for plasma physics research, contrast is one of the most important properties of the laser pulse. Various pulse cleaning techniques such as double CPA [5], XPW [6] and the use of plasma mirrors [7] can significantly improve the contrast on timescales from nanoseconds down to tens of picoseconds, but they become ineffective closer to the main pulse. For this reason it is important to understand the origins of the coherent pedestal (CP) and to find ways of reducing it. The design of the Astra pulse stretcher allowed us to separate the effects of different optical components, and show that the majority of the CP originates from the stretcher gratings
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