Modeling the response of a laser Doppler vibrometer to photoacoustic signal from solids

Different techniques for photoacoustic signal detection have been developed since its inception as a spectroscopic method. Detection tools such as microphones, piezoelectric sensors, laser beam deflection systems, and more have been used to study the response of different materials to photoacoustic excitation. The authors have proposed a method of detection of the photoacoustic signal from solids using a laser Doppler vibrometer (LDV). An analytical model of the phenomena underlying the change in phase of a LDV probe beam resulting from the photoacoustic effect from a condensed sample has been constructed. The model takes into account two phenomena responsible for changing phase of the LDV probe beam. The two phenomena are the surface vibrations caused by the periodic heating of the solid sample, and the fluctuations of index of refraction in air caused by the temperature variations and acoustic waves. Experimental verification of the model is discussed.