Abstract

The apparatus employed consists of a laser as radiation source, a cylindrical resonator, and the signal processing system. The 3,39 µm or 1,15 µm beam of a He-Ne laser was intensity modulated by a chopper. The chopper frequency was continuously varied in an interval of 100 Hz around the selected acoustic resonance. In most measurements the first radial mode of the cylindrical sample cell was excited. The pressure change in the cell was detected with a small electret microphone. The microphone signals were preamplified and then a lock-in analyzer was employed for further signal processing. Both the linear change of the chopper frequency and the corresponding microphone signal were recorded simultaneously with a two channel recorder. It was possible, to make several succesive runs through the selected frequency interval to monitor a shift of the resonance frequency. In the dynamic mixing experiments, the shift of the resonance frequency was recorded as a function of time; in the energy transfer studies, the variation of the resonance frequency as a function of pressure was observed.

© 1981 Optical Society of America