Finite size compression gratings in a large aperture chirped pulse amplification laser system.

A simple model is presented to calculate the effects of the finite size of the diffraction gratings in the compressor of a chirped pulse amplification laser system. A wavelength-dependent clipping at the second grating alters the spectral distribution of the compressed pulses, affecting their time domain as well as their spatial distribution in the focal plane. Laser parameters of paramount importance to laser/plasma interaction experiments such as peak intensity, pulse duration, and prepulse levels are affected by the compressor design. Calculations of the effect of spectral clipping on these parameters for Gaussian, sech(2), and top-hat input spectra are discussed, and the benefit of double-pass compared with single-pass compression is also investigated. As an example, with 300-mm gratings and single-pass compression, for a sech(2) spectrum the pulse length of a 400-fs pulse increases to 459 fs, the peak intensity decreases by 25%, and the focal spot size increases by 8% because of the finite size of the gratings.