研究了中心对称晶体中的三阶非线性频率转换, 并在这类晶体中实现了紫外激光的有效输出.确定了负单轴晶体的相位匹配角公式及相应的相位匹配角.选择带有离域共轭π键的冰洲石晶体和α-BBO晶体进行实验.以飞秒激光作为基频光, 在Ⅱ类相位匹配方式下, 利用α-BBO晶体获得了最高单脉冲能量为37.6 μJ的266 nm紫外三次谐波, 最高转换效率为2.5%; 利用冰洲石晶体获得了最高单脉冲能量为19.3 μJ的266 nm紫外三次谐波, 最高转换效率为1.25%.该研究验证了利用中心对称晶体的三阶非线性效应直接获得紫外激光的可行性和获得深紫外激光的可能性, 为紫外非线性晶体的探索和深紫外激光的研究提供参考.

A simple one-step direct third-order nonlinear frequency conversion process in centrosymmetric crystals was studied, and an efficient third-harmonic generation in UV region was obtained. The expressions of phase-matching angles were determined. α-BBO crystal and the calcite crystal which both have the delocalized π bond were selected in our experiment. In type-Ⅱ phase-matched, the maximal output energy was 19.3 μJ and the maximal conversion efficiency was about 1.25% at 266 nm in calcite crystal, while the value was 37.6 μJ and 2.5% in α-BBO crystal. These results indicate the feasibility of direct third-harmonic generation in UV region, the possibility of direct third-harmonic generation in deep-UV region through centrosymmetric crystals, and also demonstrated a succinct and efficient way to generate deep-UV laser and a development direction of nonlinear crystals in UV region.