摘要
Photoacoustic signals generated in liquids are generally described with a wave equation of forced motion for which source terms are incident photoenergy. As a concrete example, the wave equation is applied to cylindrical cells, and photoacoustic signals are analyzed as a function of light modulation frequency using the assumption that the thermal diffusion length is negligibly smaller than the radius of the incident laser beam which has a Gaussian distribution. Experimental results show a monotonic decrease with increasing frequency under 10 kHz and resonance peaks beyond the 10-kHz region. These can be explained by theoretical analysis. The monotonic decrease is caused by decreased photoenergy with increasing light modulation frequency and number of the thermoelastic wave modes in the cell. The peak at 153 kHz is a resonance of the thermoelastic wave in the cell, while the other peaks correspond to structural resonance of the entire cell body and to the electrical resonance of the piezoelectric transducer.