利用晶体拼接实现大口径会聚光束三倍频

Frequency tripling of convergent beam with large diameter employing tiling crystals

惯性约束聚变激光驱动器中,熔石英透镜的紫外激光损伤问题一直是限制其负载能力提升的重要因素。对此提出了一种新的大口径光束三倍频构型方案,将三倍频晶体置于聚焦透镜之后,在基频光和倍频光的会聚过程中实现和频。大口径会聚光束的入射角度达36.35 mrad,为满足相位匹配条件,三倍频晶体采用相位匹配接受角度更大、损伤阈值更高的LBO晶体。理论分析表明,3块切割角度不同的LBO晶体拼接即可满足会聚光束相位匹配容忍角的要求。原理性实验也验证了该方案的可行性。该构型不仅能规避熔石英透镜的紫外激光辐照,提升激光驱动器的负载能力,而且能突破LBO晶体的口径受限问题。

In inertial confinement fusion laser driver, ultraviolet laser damage of fused silica lens is an important limiting factor for lifting load capability of the laser driver. Considering the above reason, a new configuration of frequency tripling is proposed to solve this problem. The frequency tripling crystal is placed on the back of the focusing lens, thus the sum frequency generation of the fundamental frequency light and doubling frequency light occurs in the beam convergence path. Incident angle of the convergent beam is up to 36.35 mrad, thus the frequency tripling crystal must have a large acceptance angle for phase matching condition. LBO crystal which also has high damage threshold is employed as the frequency tripling crystal. Theoretical analysis indicates that three tiled LBO crystals with different cutting angles will meet the requirement of phase matching and principle experiments also supported this scheme. By employing this configuration, the fused silica lens will only be irradiated by fundamental frequency light and doubling frequency light and its damage threshold will be improved, thus the load capability of the laser driver will be lifted. At the same time, the limitation of growth size with LBO crystal will be broke through.