Ultra-short laser pulse formation by parametric Raman scattering

最近，基于受激拉曼散射的超短激光脉冲产生技术受到了特别的关注。但是，目前产生的光谱线总数比理论预测的要少。这种现象可以用强度相关拉曼转换引起的激光豆衍射来解释。为了抑制衍射效应，增加拉曼光谱线的数量，其中这些光谱线具有相似的强度，采用空心芯光纤。这种光纤相互作用区域的方案，是小斯托克斯位移介质的高频双谐波激励。这项工作的主要内容是增加了光谱线的数量，其中每条光谱线的强度相同，并消除了衍射效应。利用石英中空光纤的紫外双谐波激光器，对氘分子旋转拉曼跃迁（J=0>2）进行共振双色激发，得到了宽拉曼多频光谱。生成了50条230 ~ 290 nm的纯旋转拉曼谱线（其中34条谱线强度在最强谱线的10%以内）。拉曼谱线的数量与理论预测一致。

Recently, the technology behind ultra-short laser pulse generation, based on stimulated Raman scattering, has been receiving a special interest. However, the total number of spectral line generated so far was smaller than the theoretical prediction. This behavior was explained by the laser bean diffraction caused by the intensity dependent Raman conversion.In order to suppress the diffraction effect and increase the number of Raman spectral lines, where these spectral lines have similar intensities, a hollow core fiber was employed. This fiber is the interaction region of the scheme, the high-frequency bi-harmonic excitation of small Stokes shift media. The main of this work was to increase the number of spectral lines, where the intensity of each spectral line is the same, and remove the diffraction effect.Broad Raman-multi-frequency spectra were generated from the resonant two-color excitation of the deuterium molecule rotational Raman transition (J=0>2), using ultraviolet bi-harmonic lasers with a quartz hollow fiber. Fifty pure rotational Raman spectral lines (34 lines that have intensity within 10% of the strongest spectral line) from 230 to 290 nm were generated. This number of Raman spectral lines was agreed with theoretical prediction.