Abstract

In certain applications of photoacoustic spectroscopy it is desirable to measure the photoacoustic signal from a liquid which is in motion. This may be the case, for example, in the study of corrosion at a solid-liquid interface. To understand how the photoacoustic signal is altered by the motion of the sample, experiments were performed on a specially constructed cell in which a flowing layer of liquid is separated from the air in the photoacoustic cell by a thin glass window. Light is absorbed by the flowing liquid sample, and the resulting temperature oscillations propagate through the glass window and into the photoacoustic chamber. When the liquid is in motion the temperature distribution is skewed in the direction of flow. Although the temperature distribution is altered, it is not immediately obvious whether the photoacoustic signal should be different, since this depends on the total heat flux into the gas, integrated over the entire sample surface area. Experimentally it is found that both the magnitude and the phase of the photoacoustic signal vary with liquid velocity. The variation is not monotonic and suggests an interpretation involving thermal-wave interference.

© 1985 Optical Society of America