TIME-RESOLVED LASER-INDUCED THERMAL GRATING EXPERIMENTS INDUCED BY SHORT-PULSE CO2-LASER RADIATION

Using a high pressure carbon dioxide laser with pulse lengths of 80 ns laser-induced thermal grating spectroscopy (LITGS) experiments have b een carried out in gas mixtures consisting of an absorbing species (et hylene) and buffer gases (nitrogen/helium) at various temperatures and pressures. The grating structure is written into the medium by absorp tion and subsequent collisional relaxation of CO2-laser radiation. Tra nsport properties in these mixtures such as thermal conductivity and t he speed of sound have been determined from the time-resolved signal g enerated by Bragg scattering of a continuous wave HeNe-laser beam off the grating structure. Accurate numerical values for transport coeffic ients are obtained from fitting analytical expressions to the measured oscillating signal traces and are compared with literature values.