Measuring nonlinear fields without diffraction correction

It is demonstrated that a hydrophone of unusual design may be exploited to perform measurements of nonlinear fields without the necessity for diffraction corrections. The design of the thin-film PVDF hydrophone is outlined, and the basic theory underlying its utility is described. Measurements are made of nonlinear propagation effects in water, and it is indicated how the B/A parameter may be relatively easily measured in liquids by means of diffraction-insensitive monitoring of harmonic generation. An extremely sensitive technique, based on the use of the Wigner distribution, for detecting incipient nonlinearity in both pulsed and continuous-wave fields is proposed