Nonlinear generation of harmonics near the focus of an acoustic lens: application to nonlinear imaging of biological media

The use of an acoustic microscope as a method for imaging the nonlinearity of thin biological samples is evaluated. Biological tissues are simulated by liquid mixtures of well-known nonlinearity, which are placed at the focal plane between two very thin mylar sheets. The experiment consists of measuring the amplitude of the second harmonic component generated near the focal point as a function of the liquid sample used. A simple theoretical model which assumes that all harmonic generation that takes place within the sample is found to be in good agreement with the experimental results. This shows that the acoustic microscope is sensitive to the nonlinearity of the sample at the focal plane