DESIGN AND ANALYSIS OF HOLOLENSES TO OBTAIN APPRECIABLE ILLUMINATION OVER THE ENTIRE IMAGE OF AN EXTENDED OBJECT FOR ITS USE IN SPECKLE METROLOGY

In this paper theoretical curves for the variation of diffraction effi ciency, of thick phase transmission hololenses recorded on dichromated gelatin (DCG), with emulsion thickness (d), depth of refractive-index modulation (Delta eta) and fringe spacing (Lambda) at lambda = 0.6328 mu m are presented. The results of a comparative study of the theoret ical and experimental variations of diffraction efficiency with a chan ge in angle of reconstruction (delta) with respect to the Bragg angle for two typical hololenses of fringe spacing Lambda = 1.222 mu m and L ambda = 1.666 mu m respectively for a fixed value of emulsion thicknes s (d = 10 mu m) and depth of refractive-index modulation (Delta eta = 0.018) are also presented. The present investigation reveals that low- thickness emulsion, high depth of refractive-index modulation and larg e fringe spacing are quite promising for recording DCG hololenses for coherent imaging systems which can provide appreciable illumination ov er the entire image of an extended object. Such lenses can be used adv antageously in a coherent imaging system for speckle metrology.