Simulation and experimental investigation of turbid medium in frequency-domain photoacoustic response induced by modulated laser

In this work, a one-dimensional (1D) photoacoustic mathematic model of turbid medium in frequency domain is presented, and it is derived from the theories of optical absorption and radiation transfer, thermal-wave diffusion and mechanical fluctuant effect. The theoretical simulations are carried out to analyze the effects of absorption coefficient, the relative position of the absorber on the amplitude and phase of the photoacoustic signal. A frequency - domain photoacoustic imaging system is developed to carry out the position scanning inspection experiments. At the fixed laser modulation frequency, the absorption property of the medium is detected according to the positive correlation between the amplitude of the photoacoustic signal and the absorption coefficient. Based on the relationship between the relative phase of the photoacoustic signal and the relative position of the medium, the depth of the optical absorber inside the turbid medium is quantitatively detected. The experiment results indicate that the amplitude and phase of the photoacoustic signal have high sensitivity to the optical absorption coefficient and structural characteristic parameters of the turbid medium.