The Influence of Angstrom-Scale Roughness on the Laser-Induced Damage Threshold of Single-Crystal ZnGeP2

Abstract

Magnetorheological processing was applied to polish the working surfaces of single-crystal ZnGeP2, in which a non-aqueous liquid with the magnetic particles of carbonyl iron with the addition of nanodiamonds was used. Samples of a single-crystal ZnGeP2 with an Angstrom level of surface roughness were received. The use of magnetorheological polish allowed the more accurate characterization of the possible structural defects that emerged on the surface of a single crystal and had a size of ~0.5–1.5 μm. The laser-induced damage threshold (LIDT) value at the indicated orders of magnitude of the surface roughness parameters was determined not by the quality of polishing, but by the number of point depressions caused by the physical limitations of the structural configuration of the crystal volume. These results are in good agreement with the assumption made about a significant effect of the concentration of dislocations in a ZnGeP2 crystal on LIDT.

Physical and Technological Aspects of Laser-Induced Damage of ZGP Single Crystals under Periodically Pulsed Laser Irradiation at 2.1 μm

“…However, the prolonged operation of powerful OPOs and OPGs/OPAs based on ZGP is limited by the laser-induced damage (LID) of this material. In accordance with the results of numerous studies [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48], the ZGP LID always occurs at the sample surface or in the sub-surface layer rather than in the bulk in samples subjected to repetitively pulsed nanosecond-pulse-width infrared radiation. A combination of factors associated with defects in the crystal structure in the sub-surface layer and the quality of polishing of the surface itself affects the LID.…”

“…There have been a number of publications on the problem of the ZGP LID induced by lasers operating at wavelengths from 1.064 µm to 10 µm [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. These studies have revealed a significant difference in the LIDT of ZGP crystals at wavelengths of 1.064 µm and 2.1 µm [31].…”

“…One of the most promising methods for improving surface quality is magnetorheological polishing [46], which is increasingly being used in the processing of laser crystals to improve the threshold of radiation resistance and reduce the level of roughness. In [47], magnetorheological processing was first used for polishing the working surfaces of a single ZGP crystal. A non-aqueous liquid with magnetic particles of carbonyl iron, with the addition of nanodiamonds, was used in the process.…”

High-Strength Optical Coatings for Single-Crystal ZnGeP2 by the IBS Method Using Selenide and Oxide Materials

“…The ZGP single crystal boule was grown by the Bridgman method in the vertical direction on an oriented seed. Working surfaces were polished by the technology described [28]. The working surfaces of the samples were processed on a 4-PD-200 (Tomsk, Russia) polishing and finishing polish machine.…”

“…In this case, the material removal was ~30 μm, which made it possible to remove the cracked layer formed in the process of cutting the crystal into oriented plates and their preliminary grinding-the polishing procedure. Next, the samples were Working surfaces were polished by the technology described [28]. The working surfaces of the samples were processed on a 4-PD-200 (Tomsk, Russia) polishing and finishing polish machine.…”