Strain analysis by one-beam laser speckle interferometry. 2: Multiaperture method.

A detailed analysis of using multiple apertures to record laser speckles for strain analysis is presented. It is shown that the basic fringe-forming mechanism is no different from that of single-aperture recording, except that at the Fourier filtering stage the diffracted light energy is concentrated at the spatial frequencies admitted by the apertures. As a result, better isothetic fringes at higher frequencies are obtainable. The concept of moiré is not utilized in the analysis. Indeed, it is shown that some of the observed phenomena cannot be explained using the moire concept. Multiaperture arrangements studied include two, three, and four apertures.