Theoretical description for the focused parametric field after inserting asample

In the parabolic and quasi-linear approximations, a theoretical description for the acoustical parametric field from a focusing source after inserting a sample is derived by using the superposition method of Gaussian beams. T his model takes into consideration the attenuation, diffraction and nonline ar effects. The numerical computations of the axial sound pressure amplitud e curves for the difference frequency sounds after the insertion of a sampl e are presented. The results indicate that this new model can be extended t o measure or image the nonlinear parameter in the focused field.