Laser-Induced Damage Threshold of Single Crystal ZnGeP2 at 2.1 µm: The Effect of Crystal Lattice Quality at Various Pulse Widths and Repetition Rates

Abstract

The ZnGeP2 crystal is a material of choice for powerful mid-IR optical parametric oscillators and amplifiers. In this paper, we present the experimental analysis of the optical damage threshold of ZnGeP2 nonlinear crystals induced by a repetitively-pulsed Ho3+:YAG laser at 2091 nm. Two types of ZnGeP2 crystals grown under different conditions were examined using the laser and holographic techniques. The laser-induced damage threshold (LIDT) determined by the pulse fluence or peak intensity was studied as a function of the pulse repetition rate (PRR) and laser exposure duration. The main crystal structure factor for a higher LIDT was found to be a reduced dislocation density of crystal lattice. The ZnGeP2 nonlinear crystals characterized by the high structural perfection with low density of dislocations and free from twinning and stacking faults were measured to have a 3.5 J/cm2 pulse fluence damage threshold and 10.5 MW/cm2 peak intensity damage threshold at 12 kHz PRR; at 40 kHz PRR the pulse fluence damage threshold increased to over 6 J/cm2, but the peak intensity damage threshold dropped to 5.5 MW/cm2.

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

“…The value of the LIDT caused by the laser at the specified surface roughness parameters was determined not by the quality of polishing, but by the number of point recesses caused by the physical limitations of the structural configuration of the crystal volume. These results are in good agreement with the assumption about the significant influence of the dislocation concentration in the ZGP crystal on LIDT put forward in [48]. Despite the fact that the sample subjected to MRP showed a significant improvement in the surface roughness parameters compared to the sample polished using traditional technology, the LIDT practically did not change.…”

“…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].…”

Crystal ZnGeP2 for Nonlinear Frequency Conversion: Physical Parameters, Phase-Matching and Nonlinear Properties: Revision

“…An important parameter is the value of the crystal laser-induced damage threshold. In this work, we do not provide data, since a detailed description of the obtained values and methods for increasing the damage threshold are given in [32,33].…”

Influence of pump source beam quality and OPO cavity resonance regime on output characteristics of mid-infrared ZGP-OPO laser

“…The optical and physical properties of ZGP crystal is used by the SNLO software [6]. The progress of the production process of ZGP crystal has led to improvement in the absorption coe cient and damage threshold; these factors have signi cantly in uence on the conversion e ciency [7][8][9][10][11].…”