离轴抽运对模式增益和光束质量的影响

Effects of the off-axis pumping beam on the gain of the oscillating modes and beam quality

在激光二极管端面抽运固体激光器中,抽运光轴线与几何腔轴之间存在一定的偏离,使基模振荡光轴线相对几何腔轴也有一定的偏离,影响激光器性能。引入偏离因子来描述抽运光轴线的偏离量和抽运功率对振荡光偏离量的影响,对模式增益和光束质量随偏离因子的变化规律做了理论分析和模拟,并以光纤耦合半导体激光器端面抽运Nd:YAG固体激光器进行了相应实验。理论与实验结果表明:在抽运功率一定时,抽运光的偏离量越小,偏离因子越小,则低阶模模式增益越大,在模式竞争中占据优势,输出激光的光束质量越好。因此,要获得高增益和光束质量较好的低阶模输出,除保证恰当的谐振腔结构外,控制抽运光的形状和偏离量也是一个重要的手段。

In laser diode end-pumping solid-state lasers,the departure existed betweem the axis of the pumping beam and that of the geometry cavity to a certain degree,which made the axis of the fundamental mode depart from the axis of geometry cavity too.It affected the performance of the lasers. The concept of the departure factor was introduced, which described the effects of the off-axis pumping beam and pumping power on the oscillating mode. The effects of the gain efficient of the oscillating modes and output beam quality on the departure factor were analyzed in theory, and the corresponding experiments were done with the fiber coupling diode lasers end-pumping Nd：YAG lasers.The theory results were in accordance with experiments.As the pumping power hold invariable, the smaller the departure quantity is, the smaller the departure factor is, and accordingly gain of lower order mode becomes higher and the output beam quality changes better. Therefore, in order to obtain the lower order mode output with higher gain and better beam quality, it is important to control the shape and the departure quantity of pumping beam besides holding proper structure of resonator.