Some limitations of pulsed optoacoustic methods for measuring weak absorption

An analysis is made of the limitations on the precision and sensitivity of pulsed optoacoustic methods for measuring weak absorption of light in matter. These limitations are associated with the electrostriction and instability of the spatial sturcture of the heating radiation. It is shown that when a pressure wave is detected by a piezoelectric ceramic transducer of finite thickness, there is a range of parameters in which the signal is independent of the size of the heating beam and the influence of the electrostriction effects can be reduced by time gating, exactly as in the case of a "thin" transducer. Experiments are reported which demonstrate that piezoelectric detection of vibrations at natural frequencies of a sample can increase 50-fold the sign–noise ratio compared with the pressure pulse detection method.