Short-Pulse, High-Energy Q-Switched Ho³⁺:LLF Laser for Precise Time-of-Flight and High-Peak-Power Applications

Due to high transmission in the atmosphere and their eye-safe nature, 2 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex> lasers are of high interest for many applications, for example LIDAR and gated viewing [1]. Further use cases are the non-linear down conversion into the 3–5 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu\mathrm{m}$</tex> range, e.g. using ZnGeP2 crystals, and material processing. While YAG offers excellent material properties as a laser host material, high-energy pulse generation is limited by its positive thermal lens. Fluoride-based host materials like <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ho}^{3+}:\text{YLF}_{4}$</tex> or <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ho}^{3+}:\text{LLF}_{4}$</tex> offer the design of laser resonators utilizing weak negative thermal lensing [2] and a longer lifetime of the exited state compared to Ho <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3+$</tex>: yag, improving efficient energy storage in the crystal. Further advantages are natural birefringence that limits depolarization losses, and a high emission cross-section [3]. Suitable laser sources have been demonstrated using fluoride crystals [4].