Effects of Laser-Modulated Particulate Incandescence on Raman Scattering Diagnostics

Laser-modulated particulate (soot) incandescence has been studied by measuring the laser-driven particle surface temperature in a propane diffusion flame as a function of laser focal flux. The experimental results display fair agreement with an analytical model of the process. Quite importantly, the absolute incandescence level displays a saturation behavior with increasing laser pulse energy. For laser Raman scattering diagnostics, this behavior means that the S/N ratio will increase with increasing laser flux level. Thus, for highest S/N ratio, it is preferable to operate at the highest possible flux short of gas breakdown and/or optical-component damage levels.