Time-Resolved Laser-Induced Thermal Grating Experiments Induced by Short Pulse CO_2-Laser Radiation

摘要

Using a high pressure carbon dioxide laser with pulse lengths of 80 ns laser-induced thermal grating spectroscopy (LITGS) experiments have been carried out in gas mixtures consisting of an absorbing species (ethylene) and buf- fer gases (nitrogen/helium) at various temperatures and pressures. The grating structure is written into the medium by absorption and subsequent collisional relaxation of CO_2-laser radiation. Transport properties in these mixtures such as thermal conductivity and the speed of sound have been determined from the time-resolved signal generated by Bragg scattering of a continuous wave HeNe-laser beam off the grating structure.