Determination of some flame parameters using laser-induced ultrasonics

A new method of combustion diagnostics is described. A technique using laser-induced coherent ultrasonic waves is applied for temperature measurement. The ultrasonic waves are generated via thermal expansion resulting from light absorption and subsequent nonradiative relaxation in an interference pattern of two crossed pulse beams split from one excitation-laser pulse. They are detected by Bragg diffraction of a probe laser. Ultrasonic velocity measurements taken on a candle flame with light absorbing soot demonstrate that localized temperature values can be estimated.