Computer-controlled performance of photoacoustic resonance experiments

Acoustic modes in a spherical resonator are excited with a chopped 3.39-μm He–Ne laser by vibrational excitation of CH4. The recording of resonance curves is completely controlled by a microcomputer. This includes repeated registration of the resonator temperature, stabilization and determination of the modulation frequency, and integration of the acoustic signal detected with an electret microphone. A detailed description of the timing of such an automatic data acquisition for high-precision experiments is given. The accuracy of the resonance method is investigated by fitting the experimental resonance curves to the corresponding line profile and performing an analysis of the errors involved.