Spectrum shaping of an all Nd:glass CPA 1–10 ps kilojoule petawatt-class laser system

Abstract

We propose a new method for the chirped pulse spectrum shaping, which is significant in chirped pulse amplification (CPA) system to compensate the gain narrowing and the gain saturation, to obtain the shortest compressed pulse, and to improve the signal-to-noise ratio (SNR) of the output, while simultaneously increasing the amplifier efficiencies. This method is based on a grating system to decompose the chirped pulse spectrum to a spatial space, a microstructure on a multilayer dielectric thin film as a functional reflector to shape the space distribution, and a synthesis system to compose this space distribution to a shaped frequency chirped pulse before incidence into the next amplifier stage. The results show that the damage threshold by the high-power laser can be enhanced, and this functional reflector can be fabricated in an easy and cheap way, in which the accuracy in lithography is 1 μm, the etching tolerance is 35 nm, and the roughness of the etching surface is 8.5 nm. In addition, the phase aberration is less than 12 mrad in the chirped bandwidth of a few tens of nanometers, and the spatial distribution of the final output almost remains. The studies show that the energy integral of the output chirped pulse is extracted 17% and 29.5% more with center and off-center modulations, respectively, compared with the normal amplification. Moreover, the SNR has enhanced to 1010:1 at 10 ps after spectrum shaping, which enhances the SNR near 1–2 orders than that without the spectrum shaping.