Laser-induced damage threshold of ZnGeP₂ crystal for (sub)picosecond 1-µm laser pulse

Abstract

The laser-induced damage threshold (LIDT) was measured for a Z n G e P 2 crystal exposed to 0.3–9.5 ps 1030-nm laser pulses. Single-pulse LIDT fluence was ∼ 0.22 J / c m 2 for the laser pulse widths of 0.3–3.5 ps and increased until 0.76 J / c m 2 for 9.5-ps pulses. Multi-pulse LIDT fluence for 0.3-ps pulses at repetition frequencies in the range of 100 Hz–1 kHz was ∼ 0.053 J / c m 2 and decreased further at higher, multi-kHz, pulse repetition frequencies. The coating of the Z n G e P 2 crystal surface with an anti-reflection multi-layer thin film increased the multi-pulse LIDT by one order of magnitude, up to 0.62 J / c m 2 (about 2 T W / c m 2 ). The significant increase in LIDT coupled with a decrease in reflection losses provides a way to cardinally improve efficiency of frequency conversion of popular 1-µm ultrashort pulses into mid- and far-IR ranges with a thin AR-coated Z n G e P 2 crystal sample.

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.…”

“…For clarity, a histogram of the LIDT of ZGP crystals, depending on the type of AR coating, is shown in Figure 4. From the results presented in Figure 4 and Table 3, which are the result of summarizing the information obtained in [42][43][44][45], the following patterns can be observed:…”

“…Comprehensive studies of the influence of the deposition parameters of AR interference coatings and film-forming materials on the LIDT of ZGP samples (manufactured by LOC) under Ho 3+ :YAG laser irradiation have been performed [42][43][44][45]. The coatings were achieved with an Aspira-200 vacuum deposition machine by ion beam sputtering (IBS).…”

“…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].…”

“…The conflicting information about the effect of interference coatings on the ZGP LIDT presented in [37,40] suggests that the different design of coatings and methods of their application on a nonlinear crystal significantly affects the efficiency of its use in OPOs. In [42][43][44][45], comprehensive studies were conducted on the influence of the parameters of the application of AR coatings and film-forming materials on the ZGP LIDT under mid-IR laser irradiation with femtosecond, picosecond, and nanosecond pulse durations.…”