CAJ | 학술논문

采用单纵模Nd:YAG二倍频激光泵浦,研究了CH4气体中的受激喇曼散射.实验发现,当激光的重复频率为2 Hz,1.1 MPa CH4中,泵浦能量为95 mJ时,后向一级斯托克斯(BS1)的量子转化效率可达73%,并且由于激光脉冲的张弛振荡,BS1的脉宽被压窄到L2 ns,峰值功率达到了泵浦光功率的2.7倍,其光束质量大大优于泵浦光.在同样条件下,而重复频率为10 Hz时,BS1的量子转化效率降低为36%,但对光束质量影响不大,这是因为BS1呈现为与泵浦光波前翻转的复制光波,可以补偿热畸变.研究结果表明,如果设计一个CH4/He混合气体的带封闭循环冷却系统的高性能630 nm喇曼激光器,可能有其实际应用价值.
채용단종모Nd:YAG이배빈격광빙포,연구료CH4기체중적수격나만산사.실험발현,당격광적중복빈솔위2 Hz,1.1 MPa CH4중,빙포능량위95 mJ시,후향일급사탁극사(BS1)적양자전화효솔가체73%,병차유우격광맥충적장이진탕,BS1적맥관피압착도L2 ns,봉치공솔체도료빙포광공솔적2.7배,기광속질량대대우우빙포광.재동양조건하,이중복빈솔위10 Hz시,BS1적양자전화효솔강저위36%,단대광속질량영향불대,저시인위BS1정현위여빙포광파전번전적복제광파,가이보상열기변.연구결과표명,여과설계일개CH4/He혼합기체적대봉폐순배냉각계통적고성능630 nm나만격광기,가능유기실제응용개치.
The conversion efficiency of stimulated Raman scattering (SRS) in CH4 is studied by using a single longitudinal mode second-harmonic Nd:YAG laser (532 nm, linewidth 0.003 cm-1, pulse-width (FWHM) 6.5 ns).Due to the heat release from vibrationally excited particles, SRS processes often suffer from the thermal defocusing effect (TDE). In view of 6.5 ns laser pulse width is much shorter than the vibrational relaxation time of CH4 molecules, TDE can only affect the SRS processes afterwards. In the cases of low laser repetition, TDE will be not serious, because it will be removed by the thermal diffusion in Raman medium before the next pulse arrives. At the laser repetition rate 2 Hz, CH4 pressure 1.1 MPa and pump laser energy 95 m J, the quantum conversion efficiency of backward first-Stokes (BS1) has attained 73%. This represents the highest first-stokes conversion efficiency in CH4. Furthermore, due to the relaxation oscillation, the BS1pulses are narrowed to about 1.2 ns. As a result, the BS1 peak power turns out to be 2.7 times that of the pump. Its beam quality is also much better and is only slightly affected by TDE. This reason is that BS1 represents a wave-front-reversed replica of the pump beam, which can compensate the thermal distortions in Raman amplify process. Under the same conditions, but pump laser repetition rate as 10 Hz, the conversion efficiency of BS1 goes down to 36% due to TDE. From this study, we expect that a well-behaved 630 nm Raman laser may be designed by using a closed CH4/He circulating-cooling system, which may have some important applications.