How the laser beam size conditions the temporal contrast in pulse stretchers of chirped-pulse amplification lasers

Abstract

In this work, we propose and verify experimentally a model that describes the concomitant influence of the beam size and optical roughness on the temporal contrast of optical pulses passing through a pulse stretcher in CPA laser systems. We develop an analytical model that is capable of predicting the rising edge caused by the reflection from an optical element in a pulse stretcher, based on the power spectral density of the surface and the spatial beam profile on the surface. In an experimental campaign, we characterize the temporal contrast of a laser pulse that passed through either a folded and an unfolded stretcher design and compare these results to the analytical model. By varying the beam size for both setups, we verify that optical elements in the near-and the far-field act opposed to each with respect to the temporal contrast and that the rising edge caused by a surface benefits from a larger spatial beam size on that surface.

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“…The remaining rising slope leading to the main pulse is clearly resolved and not masked by the limitations of the measurement tools. Its origin has recently been shown to lie in the combination of beam size and surface imperfection of the stretcher setup necessary for the CPA scheme and its mitigation and control is still being further investigated [32][33][34] .…”

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