高功率紧凑型Tm:YAG激光实验装置：设计与性能分析

高功率紧凑型Tm:YAG激光实验装置如图1所示，主要由一个三向侧面抽运结构的激光模块和两个平面镜组成。Tm:YAG晶体棒的尺寸为φ3 mm×74mm，晶体的掺杂区域仅有36mm，Tm3+的掺杂原子数分数为3%。为了减少重吸收损耗的热效应，棒两端键合有19mm未掺杂的YAG。晶体棒端面均镀有2020nm增透膜，以提高透过率。晶体棒被安装在被放置在内径为4.5mm，厚度为1mm的石英管中。

激光模块中，三个LD Bar条（Focus Light, 美国）呈120°中心对称分布，每个Bar条的最大抽运功率均为220W，并且与晶体棒轴线的距离为6mm。LD Bar条的中心波长为780nm，对应于Tm:YAG较宽的吸收带，因此，随着驱动电流的增加，晶体的吸收系数变化较小，晶体棒内抽运光仍可以保持均匀分布，从而最大限度地利用增益介质体积。此系统采用了单通道水冷的结构设计，利用一个水冷机同时对LD Bar条和Tm:YAG晶体进行冷却。实验中LD Bar条和晶体棒的冷却水流量分别为4.5L/min和6.5L/min.

腔镜M1镀有2020nm高反膜，M2为耦合输出镜，实验中选择的输出透过率为7.8%，总腔长为88m。

图1：高功率紧凑型Tm:YAG激光实验装置示意图，LD：激光二极管，M1、M2：平面反射镜，Tm:YAG：铥掺杂钇铝石榴石晶体棒。

The high-power compact Tm:YAG laser experimental device shown in Figure 1 consists of a laser module with a three-way side-pumping structure and two flat mirrors. The size of the Tm:YAG crystal rod is φ3 mm × 74 mm, and the doped region of the crystal is only 36 mm, with a doping atomic fraction of 3% for Tm3+. In order to reduce the thermal effect of reabsorption loss, there is a 19 mm undoped YAG at both ends of the rod. The end faces of the crystal rod are coated with 2020 nm anti-reflection film to improve the transmittance. The crystal rod is mounted in a quartz tube with an inner diameter of 4.5 mm and a thickness of 1 mm.

In the laser module, three LD Bar strips (Focus Light, USA) are symmetrically distributed at 120°, with a maximum pumping power of 220 W for each Bar strip, and a distance of 6 mm from the axis of the crystal rod. The center wavelength of the LD Bar strip is 780 nm, corresponding to the wider absorption band of Tm:YAG. Therefore, as the driving current increases, the absorption coefficient of the crystal changes slightly, and the pumping light inside the crystal rod can still be evenly distributed, maximizing the utilization of the gain medium volume. This system adopts a single-channel water-cooling structure design, using a water cooler to cool both the LD Bar strip and the Tm:YAG crystal at the same time. The cooling water flow rates for the LD Bar strip and the crystal rod in the experiment are 4.5 L/min and 6.5 L/min, respectively.

Mirror M1 is coated with a 2020 nm high-reflection film, and M2 is a coupling output mirror. The output transmittance selected in the experiment is 7.8%, and the total cavity length is 88 m.