LD End-Pumped Tm:YLF Innoslab Lasers with Various Doping Concentrations
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Journal of Russian Laser Research, Volume 41, Number 5, September, 2020
LD END-PUMPED Tm:YLF INNOSLAB LASERS WITH VARIOUS DOPING CONCENTRATIONS Haonan Zhang,1,2 Miaomiao Lin,1,2 Zhaopeng Xu,1∗ Yefei Mao,2† and Lei Wang2 1 School
of Information Science and Engineering Yanshan University Qinhuangdao, 066004, China
2 Qian
Xuesen Laboratory of Space Technology China Academy of Space Technology Beijing, 100094, China
∗ Corresponding
author e-mail: xuzhaopeng1 @ 163.com author e-mail: maoyefei @ qxslab.cn
† Corresponding
Abstract We report on high-power laser-diode (LD) end-pumped Tm:YLF innoslab lasers with different doping concentrations of 2, 2.5, and 3 at.% with a single-end 792 nm LD stack. After series of experiments, we conclude that 3 at.% Tm:YLF lasers can produce a maximum output power of 84.7 W; this value is higher than that of the lasers with two other doping concentrations at the same incident pump power equal to 348 W. The corresponding optical-to-optical efficiency and the slope efficiency with respect to the absorbed pump power are 27.9% and 52.7%, respectively. The emission wavelength is 1909.6 nm with a FWHM of 1.3 nm. The M2 factor of the output power at 55 W is 498 along the x axis and 1.8 along the y axis. The shape of the output light is a rectangular spot, which is appropriate for pumping Ho-doped slab lasers.
Keywords: innoslab lasers, end-pumped laser, various doping concentrations.
1.
Introduction
2 μm eye-safe lasers, being located in the atmospheric window, are widely applied in the field of industry, medicine, military, and science [1–3]. The Ho3+ -doped crystal is a preferable material for producing high-power 2 μm lasers due to the higher emission cross section. However, the Ho:YAG laser directly pumped by laser diode is inefficient and unable to provide high-power output. Since the Tm:YLF laser emission peak is located in the absorption peak of the Ho:YAG crystal [4], high-power Tm:YLF lasers are commonly used to pump Ho:YAG lasers. In addition, Tm:YLF crystals have relatively longer upper-level lifetime and a broader absorption band at 792 nm; thus, it is suitable for direct laser-diode pumping. Meanwhile, YLF is the birefringent crystal, which can produce linear polarized laser, and the refractive index of YLF decreases with increase in temperature. According to this property, this crystal can be used as a negative thermal lens to partly compensate the thermal lens effect of the crystal [5]. Therefore, Tm:YLF lasers are usually served as excellent pump sources for Ho:YAG lasers. A Tm:YLF laser is generally considered as a quasi-three-level system with cross-relaxation and energy transfer up-conversion (ETU) between adjacent ions. These two transition processes have important effect on the laser performance. ETU is a loss mechanism, which limits the number of excited-state ions Manuscript submitted by the authors in English on July 25, 2020. c 2020 Springer Science+Business Media, LLC 1071-2836/20/4105-0533
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Journal of Russian Laser Research
Volume 41, Number 5, September, 2020
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