Analytical analysis of the decrease in the focal intensity of a femtosecond laser pulse caused by an imperfect surface of compressor diffraction gratings

TL;DR

This paper derives an analytical model for how imperfect diffraction gratings in a femtosecond laser compressor affect the focal intensity, highlighting the role of angular chirp and grating surface quality.

Contribution

It provides an analytical expression linking grating surface imperfections and spectral bandwidth to focal intensity reduction, and suggests a simple rotation to mitigate effects.

Findings

Angular chirp caused by grating imperfections significantly reduces focal intensity.

Rotating the fourth grating optimally can mitigate intensity loss.

Surface roughness and spectral bandwidth jointly influence focal intensity behavior.

Abstract

An analytical expression for the focal intensity of a laser pulse was obtained for an asymmetric out-of-plane compressor with gratings of arbitrary surface shape. The focal intensity is most strongly affected by the linear angular chirp caused by the spatial shift of different frequencies on the second and third gratings. The chirp can be eliminated by simply rotating the fourth grating by an optimal angle, which significantly reduces the requirements for the grating quality. It is shown that the decrease in the focal intensity depends on the product of grating surface rms and pulse spectrum bandwidth. With low-quality gratings, spectrum narrowing would not reduce focal intensity; contrariwise, it may even slightly increase it.