Confocal Beam Formation for an Oblique Scanning Acoustic Microscope

Abstract

Confocal converging non-apertured acoustic beams are desirable in oblique offspecular reflection microscopy and for observing signal intermodulation in microscopy. Our experience has shown that optimal coincidence of focus and axial intersection of the beams requires rather specific choices of dimensional parameters. We have studied acoustic beam formation by analysis and by computation using the Huygens-Fresnel principle and show that confocal operation from a simple solid lens substrate is possible. We also have found that a strong transverse component of field exists in the focal region of highly convergent beams and we believe that the transverse component is important in intermodulation and in understanding Rayleigh wave ineraction.