提出了将饱和吸收Cr4+∶YAG晶体被动调Q开关同时作为布儒斯特片在三镜V型折叠谐振腔中起像散补偿作用的腔内倍频设计方案。在连续激光二极管端面抽运情况下,给出了V型谐振腔结构光束束腰半径和位置、像散补偿Cr4+∶YAG晶体的厚度和谐振腔折光角度的设计方法以及计算公式。采用周期极化铌酸锂晶体作为倍频元件,由于谐振腔内的基波和谐波具有相同的偏振方向,避免了腔内双折射引起的绿光噪声问题,得到了输出稳定的序列脉冲。在连续抽运功率为500 mW时,得到了平均功率42.7 mW的脉冲绿光输出。

A folded 3-mirror laser resonator in which a Cr4+∶YAG crystal is employed as a saturable absorber for passively Q-switching and a Brewster plate to compensate astigmatism was designed. The resonator has small radius of laser waists, so it is very suitable to the laser diode pumped intercavity frequency-doubling lasers with quasi-phase-matched frequency-doubler. The expressions to calculate the radius and the place of laser waist, curvature of the mirrors used in the resonator, the thickness of a Brewster plate, and folding angle of the resonator were presented. The performance of continous-wave laser diode pumped passively Q-switched PPLN intercavity frequency-doubling laser with the folded 3-mirror laser resonator was investigated. As the result that both fundamental and second harmonic waves have the same polarization, no green-noise problem exists. The pulse series of laser output are stable. The laser has the average output power 42.7 mW under the CW input power 500 mW.