| Stimulated Raman scattering?SRS?provides an important method for laser beam wavelength conversion.SRS from gas can meet one's need for diverse wavelength in the practical application because gas media can tolerate higher pump power than solid media and gas species with Raman activity are rich.More importantly,the laser with wavelength in the middle-infrared band can be obtained since the high-order stokes light from gas SRS has a larger frequency shift.In this paper we increase the interaction light path between pump laser beam and gas media by designing and fabricating the long light-path SRS cell,so high order Stokes output efficiency is improved by this long light-path SRS cells.Detailed results in this work are listed as below:?1?The efficiency of high order stokes SRS in CH4 and D2 are studied by using long light-path SRS cells.The influence of gas pressure,pumping energy and light-path length on high order stokes are examined,and the 1st Stokes and 2nd Stokes outputs are compared.?2?Backward SRS in CH4 are studied,and the mechanism of backward SRS generation and gain are analyzed.?3?The effect of the different light paths on the efficiency of the high order stokes SRS are analyzed and the effect of the cooling fan on the thermal effect in the experiment is also explored.Finally,we obtain the following experimental results that the 2nd Stokes photon conversion efficiency reaches 17.2 % in CH4,and the wavelength is 2804 nm;The 2nd Stokes photon conversion efficiency reaches 24.9 % in D2,and the wavelength is 2920 nm. |
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