Spatial Filter with Volume Gratings for High-peak-power Multistage Laser Amplifiers

TL;DR

This paper introduces a novel spatial filter using volume phase gratings with angular selectivity to improve high-peak-power multistage laser amplifiers, avoiding damage caused by traditional pinhole filters.

Contribution

It proposes a new spatial filtering method based on Bragg diffraction gratings, enhancing stability and performance in high-energy pulsed laser systems.

Findings

Angular spectrum bandwidth less than 160 urad.

Effective suppression of harmful focusing effects.

Stable diffraction efficiency under high-pulse-energy conditions.

Abstract

The regular spatial filters comprised of lens and pinhole are essential component in high power laser systems, such as lasers for inertial confinement fusion, nonlinear optical technology and directed-energy weapon. On the other hand the pinhole is treated as a bottleneck of high power laser due to harmful plasma created by the focusing beam. In this paper we present a spatial filter based on angular selectivity of Bragg diffraction grating to avoid the harmful focusing effect in the traditional pinhole filter. A spatial filter consisted of volume phase gratings in two-pass amplifier cavity were reported. Two-dimensional filter was proposed by using single Pi-phase-shifted Bragg grating, numerical simulation results shown that its angular spectrum bandwidth can be less than 160urad. The angular selectivity of photo-thermo-refractive glass and RUGATE film filters, construction stability, thermal stability and the effects of misalignments of gratings on the diffraction efficiencies under high-pulse-energy laser operating condition are discussed. Keywords: spatial filter, pinhole spatial filter, RUGATE filter, angular selectivity of volume phase grating, Pi-phase-shifted Bragg grating, high-energy pulsed laser, multi-pass laser amplifier