Dependence of laser-induced fluorescence on gas-dynamic fluctuations with application to measurements in unsteady flows

Acoustic waves produced in a gas-filled cell under conditions of resonance are used to study the relation between laser-induced fluorescence and a known disturbed gas state. The objective of the work is to test the theory and to develop a method for making a point measurement of fluctuating pressure in a compressible flow. Iodine was used as a seed gas in nitrogen and the iodine was excited by the 514.5 rim. ouput of an argon-ion laser. The experiments confirm the theoretical prediction that the fractional change in the fluorescence signal is approximately equal to the fractional change in the pressure, but with an opposite sign, when the laser wavelength is tuned to the iodine absorption line center and the pressure is high. Pressure signals of the order of one percent of the undisturbed pressure (40 to 760 Torr) were measured in the test cell using the fluorescent signal.