SRS conversion efficiency assessment of a single cell Raman gas mixture for DIAL ozone lidar

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 (H ₂) and methane (C H 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 H ₂:C H ₄ emits a coaxial beam of two wavelengths, 288.4 nm (C H ₄) and 299.1 nm (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 (H ₂:C H 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.