报道了一台基于Nd:YAG/Cr:YAG键合晶体的全固态355 nm紫外(UV)激光器的设计及实验结果。采用平-平腔结构获得高峰值功率、小束腰的1064 nm基频光。在谐振腔外,未聚焦的1064 nm基频光经KTP晶体倍频产生532 nm波长激光,二者再经LBO晶体和频获得355 nm紫外激光输出。实验中发现尽管Nd:YAG与Cr:YAG都是各向同性晶体,但在特定情况下输出的1064 nm基频光具有近似线偏振的特性,此特性可以有效地增加二次谐波产生(SHG)时基频光的利用率,从而提高整台激光器的转换效率。而基频光的谱线宽度及发散角也影响二次谐波及三次谐波产生(THG)的转换效率,需使其尽量在晶体的允许带宽及允许角范围以内。综合这几点因素,对激光谐振腔进行了仔细设计。当激光二极管(LD)抽运功率为8 W,激光器运行稳定时,基频光峰值功率达28 kW,最终获得平均功率为124 mW的355 nm紫外激光。

Design and experiment results of an all solid-state 355 nm ultraviolet (UV) laser based on Nd:YAG/Cr:YAG composite crystal are reported. The 1064 nm fundamental frequency radiation of high peak power and small waist was generated by plano-plano cavity. Outside the cavity, the fundamental beam was passed through a KTP crystal and a LBO crystal without been focused. The KTP crystal was used for frequency doubling of the 1064 nm radiation to generate second harmonic 532 nm radiation, and the LBO crystal was used as a sum-frequency of the 1064 nm radiation and the 532 nm radiation to generate 355 nm radiation. Although both Nd:YAG and Cr:YAG are isotropic crystals, the 1064 nm fundamental frequency radiation was near-linearly polarized in particular situations. This characteristic is benificial for the conversion of fundamental radiation to second harmonic generation (SHG) and enhance the conversion efficiency of the whole laser system. And divergence angle and bandwidth of the fundamental beam related to conversion efficiency of both SHG and the third harmonic generation (THG) should be within the range of crystal acceptance angle and acceptance bandwidth. Considering these factors, the cavity had been designed carefully. When the laser diode (LD) pump power is 8 W, the peak power of the fundamental beam was 28 kW, and finally, the 355 nm radiation average power of 124 mW was achieved.