HOLOGRAPHIC DISPLACEMENT MEASUREMENTS IN FLUID AND SOLID MECHANICS - IMMUNITY TO ABERRATIONS BY OPTICAL CORRELATION PROCESSING

The measurement of three-dimensional vector displacements in fluid and solid mechanics using holography is severely restricted by aberration which prevents the reconstruction of a high fidelity real image. This paper demonstrates how immunity to aberrations can be achieved throug h complex (i.e. optical) autocorrelation of the wavefront amplitude di stribution emanating from a region of the real image. Theory is presen ted which shows that, by the use of optical autocorrelation, aberratio n associated with high numerical aperture (NA) holographic recordings necessary for good 'depth' resolution is, within well defined limits, of no consequence. Further to this, a three-dimensional vector displac ement is obtained from just one 'view' into the real image.