| Stimulated Raman scattering (SRS) is a stimulated-scattering process with some characteristics same to laser radiation, which can be used to generate new coherent radiation sources and has long been shown to be an important method to shift laser wavelength. SRS in gaseous CH4, H2 and O2 have been investigated by using a pulsed Nd:YAG laser at 355 nm in two different bandwidth cases in this dissertation. Its main content is as follows:In broad pump linewidth (1 cm-1) case, backward stimulated scattering was completely suppressed since their gain coefficients are all much smaller than that for forward SRS. In this case, we have mainly studied the energy distribution among various-order Stokes of forward SRS in gas medium and the variation of their conversion efficiencies with gas pressure and pump energy. Furthermore, the effect of four-wave mixing on high-order Stokes generation and the influence of inert gas on multi-order Stokes conversion were also discussed in detail. For CH4, H2 and O2, their maximum quantum conversion efficiencies for first Stokes are respectively 79%, 83% and 29.6%, which are almost higher than those reported in previous literatures.In narrow pump linewidth (0.003 cm-1) case, since the gain coefficients for backward stimulated scattering increase highly, thus a relatively high conversion efficiency for backward scattering can be obtained. For CH4 and H2, backward scattering is mainly backward SRS and their maximum quantum conversion efficiencies can arrive at 64.7% and 58.6%, respectively; while for O2, it is mainly stimulated Brillouin scattering and its maximum quantum conversion efficiencies is about 74%. In this case, we have mainly investigated the competition between forward and backward stimulated scattering and also discussed the influence of the thermal defocusing effect and inert gas on this competition. In addition, a... |
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