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Abstract
A single Raman cell configuration useful for DIAL ozone lidar is designed and optimized. The conversion efficiency and flexibility of using a single Raman cell filled with a mixture of high pressure Raman active gases hydrogen (${{\rm H}_2}$) and methane (${{\rm CH}_4}$) have been examined and reported. The stimulated Raman scattering (SRS) conversion efficiency of Raman active gases with different total cell pressures and the volume mixing ratio excited with a focused, frequency quadrupled Nd:YAG laser with a maximum pulse energy of 25 mJ and a pulse duration of 10 ns at 100 Hz repetition rate are examined in detail. The gas combination of ${{\rm H}_2}{:}{{\rm CH}_4}$ emits a coaxial beam of two wavelengths, 288.4 nm (${{\rm CH}_4}$) and 299.1 nm (${{\rm H}_2}$), with a maximum total conversion efficiency of about 45%. The optimum volume mixing ratio for generating the required wavelength pair with almost equal energies is found to be 2:1 (${{\rm H}_2}{:}{{\rm CH}_4}$) at a total cell pressure of 18 bar. The contribution of cascade Raman scattering (CRS) and four-wave mixing (FWM) to the higher order Stokes lines is examined. The laser attenuation due to soot formation under various mixing ratios in the cell is also presented.
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