Measurement of the mechanical amplitude and phase of transient surface acoustic waves using double-pulsed TV holography and the spatial Fourier transform method

Abstract

We present a technique to calculate the mechanical amplitude and phase of an ultrasonic plane wavefield of nanometric amplitude that propagates on a surface. Our aim is to detect perturbations of the initially smooth wavefronts that indicate the presence of flaws in the material. We use bursts of Rayleigh waves and a double-pulsed TV Holography system that records two correlograms separated down to 1.5 microseconds. The phases of the correlograms are calculated separately using the spatial Fourier transform method (SFTM), and subtracted. In the resultant phase map, the field of instantaneous displacements of the surface (that comprises several periods of the surface acoustic wave) acts as a modulated spatial carrier, now related to the mechanical phase and amplitude, that are extracted applying the SFTM again.