Continuous-Wave and Pulsed Operation of a Ring Laser Cavity with The Ho:YLF and Ho:YAG Crystals
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Journal of Russian Laser Research, Volume 41, Number 5, September, 2020
CONTINUOUS-WAVE AND PULSED OPERATION OF A RING LASER CAVITY WITH THE Ho:YLF AND Ho:YAG CRYSTALS Yunpeng Wang,∗ Xinyu Fang, Youlun Ju, Tongyu Dai, and Dong Yan National Key Laboratory of Tunable Laser Technology Harbin Institute of Technology Harbin 150001, China ∗ Corresponding
author e-mail:
yunpengwang2020 @ 163.com
Abstract We demonstrate a 2.5 m ring laser with the Ho:YAG and Ho:YLF crystals end-pumped by the Tmdoped fiber laser. In the Ho:YAG laser, the continuous-wave (CW) output power was 4.72 W at a wavelength of 2090.8 nm when the incident pump power was 21.5 W, which corresponded to a slope efficiency of 26.3%. For the Q-switched operation with the 100 Hz pulse repetition frequency (PRF), an output energy of 5.16 mJ and a pulse width of 125.6 ns were achieved at a pump power of 9.53 W. In the Ho:YLF laser, up to a 4.14 CW output power was realized under an incident pump power of 22.3 W, which corresponded to a slope efficiency of 27.3%. At the 100 Hz Q-switched operation, the output energy was 4 mJ and the corresponding pulse width was 165.4 ns, when the pump power was 9.86 W.
Keywords: ring laser, Ho:YAG laser, Ho:YLF laser, Q-switched operation.
1.
Introduction
2 μm solid-state lasers have drawn more attention in various applications, such as differential absorption lidar (DIAL) [1,2], coherent Doppler lidar [3,4], medicine [5], and nonlinear frequency conversion for pumping optical parametric oscillators (OPOs) [6] due to their eye-safe characteristics. Traditionally, the 2 μm laser is achieved employing the Tm and Ho codoped materials pumped by 790 nm semiconductor lasers. However, the codoping technique do not have the capability to realize higher-energy laser output due to the up conversion losses at the high-pumping condition [7, 8]. There is also a thermal load at the up conversion process in the Tm- and Ho-codoped crystals [9]. An effective method to overcome these difficulties from a Tm- and Ho-codoped system is to directly provide the pumping of the Ho-doped media by an excellent 1.9 μm Tm-doped solid-state or fiber laser. Ho:YAG and Ho:YLF crystals are prospective competitors to obtain a 2 μm high-energy and high-power laser because of low quantum defects, insensitive to temperature and characterized by the emission cross section several-times higher than that of Tm-doped crystals [10]. In 2005, using a Tm-doped fiber laser as the pumping source, Dergachev et al. reported a high-energy Ho:YLF laser [11]. At a 200 Hz Q-switched operation, the maximum single pulse energy was 45 mJ and the corresponding pulse width was 20 ns. In 2006, So et al. proposed a CW compact Ho:YAG laser side-pumped by an intracavity Tm:YLF slab laser [12]. The maximum output power at 2.1 μm was 14 W, which corresponded to a slope efficiency of 16%. Manuscript submitted by the authors in English on August 2, 2020. c 2020 Springer Science+Business Media, LLC 1071-2836/20/4105-0539
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Journal of Russian Laser Research
Volume 41, Number 5, September, 20
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