对激光二极管端面泵浦Cr4+∶YAG被动调Q Nd∶YAG激光器输出特性进行了实验研究.实验研究发现, 激光器输出功率及脉冲重复频率随谐振腔长度增大而增大.为解释这一实验现象, 测量了泵浦光斑在激光晶体内尺寸, 同时计算了激光晶体及Cr4+∶YAG晶体内的基模激光光斑半径随谐振腔长度变化.分析结果表明：激光晶体内泵浦光斑尺寸远小于激光晶体内基模光斑半径, 腔模间交叠效率较低; 当腔长增加时, 激光晶体内的基模激光光斑减小, 腔模间交叠效率增加, 从而导致输出功率及脉冲重复频率随腔长增加而增加; 另外, Cr4+∶YAG晶体内光斑半径也随谐振腔长度减小, 引起Cr4+∶YAG晶体漂白时间缩短, 导致脉冲重复频率随腔长增加而增加.

The output characteristics of a LD end-pumped Cr4+∶YAG passively Q-switched Nd:YAG laser are experimentally investigated. The experiment shows that the output power and pulse repetition rate increases with the cavity length. To explain above experiment phenomenon, the pump laser beam sizes in the Nd:YAG crystal are measured, and the fundamental mode laser beam radius in the Nd∶YAG crystal and the Cr4+∶YAG crystal are calculated. The investigations show that two reasons result in the output power and pulse repetition rate increasing with the cavity length. Firstly, the pump beam size in the Nd∶YAG crystal is far less than the fundamental mode laser beam in the Nd:YAG crystal. The overlap efficient between pump and the laser beam is low. With the cavity length increasing, the fundamental mode laser beam in the Nd∶YAG crystal decreases, which results in the overlap efficient between pump beam and the laser beam increasing. So the output power and the pulse repetition rate increase with the cavity length increasing. Secondly, the laser beam radius in the Cr4+∶YAG crystal also decreases with the cavity length, which shorten the time interval between two bleaching of the Cr4+∶YAG crystal. So the pulse repetition rate increases with the cavity length.