研究了脉冲Nd:YAG激光(355 nm)泵浦的甲烷中多级Stokes光的产生和惰性气体对其转换效率的影响,其中一级和二级Stokes光的最大能量转换效率分别可达71%和38%(对应量子效率为79%和48%),大大高于已往文献报道的20%.在0.5 MPa下,可同时获得322 nm(3.6%),355 nm(24.5%),396 nm(24.3%),448 nm(22.3%)和515 nm(9.3%)的多波长输出.甲烷压力对多级Stokes转换有显著影响:高气压利于产生高效的一级Stokes光,而低气压则适合于高级Stokes光的产生.根据级联受激拉曼散射(SRS)和四波混频(FWM)理论对实验结果进行了分析,结果表明甲烷中高级Stokes光的产生是SRS和FWM协同作用的结果.加入的氦气增强了甲烷中Stokes光的转换效率,而氩气的作用恰恰相反,利用热透镜效应可以很好地解释这些现象。

Multi-order Stokes generation in pure CH₄ and its He/Ar mixture pumped by a pulsed Nd:YAG laser at 355 nm were investigated. Maximum energy conversion efficiencies as high as 71% and 38% (i.e. quantum efficiency of 79% and 48%), much higher than those reported in previous literatures, were attained under 2.5 MPa and 1 MPa for the first and second Stokes respectively. Under 0.5 MP_a CH₄, significant multi-wavelength outputs could be obtained with energy distribution of 3.6% at 322 nm, 24.5% at 355 nm, 24.3% at 396 nm, 22.3% at 448 nm, and 9.3% at 515 nm. High-pressure CH₄ was good for highly efficient first Stokes conversion, while low-pressure CH₄ was suitable for higher order Stokes generation. The experimental results were analyzed in detail in terms of cascade stimulated Raman scattering and four-wave mixing, indicating that such efficient high-order Stokes generation in CH₄ should be the result of their cooperative effect. The addition of He enhanced the Stokes conversion efficiencies, while Ar acted adversely,which could be explained by the thermal lens effects.