报道了一种高效率、结构紧凑型的激光二极管(LD)侧面抽运Nd:YVO4板条激光放大器。主振荡器为被动调Q微片激光器，在重复频率为20 kHz时，种子激光为平均功率为0.5 W，脉冲宽度为2.371 ns的基模激光。为了匹配抽运光模体积，实现高的能量提取效率和高增益放大，并减小热透镜效应，设计了一种分别对抽运光和种子激光进行整形的激光放大器。采用柱透镜对LD单bar发射的抽运光进行整形，同时采用焦距为75 mm的球透镜组对一通放大种子激光进行压缩；采用焦距为60 mm的柱透镜组对二通和三通放大种子激光进行压缩，以匹配抽运光的模体积。在重复频率为20 kHz时，实现了平均功率为5.5 W，脉冲宽度为2.5 ns，光束质量因子M2为1.5的激光输出，能量提取效率大于14%。

A compact laser diode side-pumped multipass Nd:YVO4 slab laser amplifier is reported. The master oscillator is a passively Q-switched microchip laser, and the seed laser with average power of 0.5 W and pulse duration of 2.371 ns is obtained in TEM00 mode when the repetition frequency is 20 kHz. In order to achieve high efficiency and high gain amplification output, we design a compact structure to collimate the pump laser and the seed laser. In order to optimize the energy extraction and reduce the thermal aberrations, the pump laser is collimated by a cylindrical microlens in the vertical direction. In order to match the horizontal gain diameter, the spherical lenses (f=75 mm) are used to focus the laser into the slab in the first pass, and the cylindrical lenses (f=60 mm) are used to focus the laser into the slab in the second and the third passes. After three-pass amplification, average output power of 5.5 W, pulse duration of 2.52 ns and M2 of 1.5 are achieved when the repetition frequency is 20 kHz, and the corresponding energy extraction efficiency is greater than 14%.