Millijoule ultrafast optical parametric amplification as replacement for high-gain regenerative amplifiers

We report on the development of an ultrafast optical parametric amplifier front-end for the Petawatt High Energy Laser for heavy Ion eXperiments(PHELIX)and the Petawatt ENergy-Efficient Laser for Optical Plasma Experiments(PEnELOPE)facilities.This front-end delivers broadband and stable amplification up to 1 mJ per pulse while maintaining a high beam quality.Its implementation at PHELIX allowed one to bypass the front-end amplifier,which is known to be a source of pre-pulses.With the bypass,an amplified spontaneous emission contrast of 4.9×10^(−13)and a pre-pulse contrast of 6.2×10^(−11)could be realized.Due to its high stability,high beam quality and its versatile pump amplifier,the system offers an alternative for high-gain regenerative amplifiers in the front-end of various laser systems.

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

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 chirped-pulse amplification 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 or an unfolded stretcher design and compare these results with 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.