355 nm脉冲激光在甲烷中的高效多波长拉曼转换
Efficient multi-wavelength Raman conversion in methane pumped by pulsed laser at 355 nm
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摘要: 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。Abstract: 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 MPa 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
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