Optoacoustic pulses in a flame

Pulsed pressure waves are produced by energy transfer from electronically excited Na or Li atoms seeded in an acetylene-air flame; the excitation is provided by a resonantly tuned, pulsed laser. Temperature increases of similar to 1 degrees within the flame produce signals easily detected by a microphone. A description of the phenomenon is given, and preliminary results are presented for two possible applications: localized speed-of-sound measurements and quenching rate determinations.