Open AccessEffects of pump pulse energy and repetition rate on beam quality in a high-power mid-infrared ZnGeP2 OPO
Author(s) -
M. Piotrowski,
Manuel A. Medina,
Martin Stevens,
G. Spindler,
Anne Hildenbrand-Dhollande
Publication year - 2021
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.414074
Subject(s) - optics , pockels effect , laser beam quality , materials science , beam (structure) , pulse (music) , laser , optoelectronics , physics , laser beams , detector
We report on changes of beam quality with rising pump pulse energy and repetition rate in a high-power mid-infrared ZnGeP 2 (ZGP) OPO in a non-planar cavity. The ZGP OPO generates 25 W in 3 - 5 μm pumped by a 10 kHz Q-switched Ho:LLF MOPA system at 2 μm. The beam quality factor increases from nearly diffraction-limited at OPO threshold to a M 2 = 1.8 at maximum pump power. The degradation can be attributed to thermal lensing and gain guiding effects in the nonlinear crystal. To discriminate between those effects, we monitored the beam quality as a function of the repetition rate at the highest pump pulse energy using a Pockels cell as a pulse picker. Therefore, the heat load inducing thermal lensing increases linearly, whereas gain guiding remains nearly unaffected. M 2 shows a minimum of 1.2 at 1 kHz, starting from 1.3 at 100 Hz and rising to 1.8 at 10 kHz. Those findings have been reproduced by numerical simulations. Further investigations show the transient evolution of beam quality, revealing the thermal lens build-up process to the steady-state.