A new photopolymer holographic recording material, ULSH-500. based on cationic ring-opening polymerization, has been further optimized to achieve low transverse shrinkage without sacrificing sensitivity. The extent of transverse (z) and lateral (x) shrinkage was determined explicitly in this study for a range of slant angles, in volume holograms which were recorded to near saturation and in holograms of low diffraction efficiency. AKX /Kx and AKZ /Kz, which represent the physical material shrinkage in the grating vector plane, were ascertained by 1) direct measurement of the differential angle changes in the reference and signal beam angles necessary to achieve Bragg matching and 2) measurement of the average refractive index. The accuracy of this method was primarily limited by the exactness in determining the angle of peak efficiency in the Bragg selectivity curve. It is demonstrated that the peak angle can be established to within a small fraction of a degree. It is shown that the assumption of anchoring and thus uniaxial shrinkage, as embodied in the conventional fringe rotation model, can not be applied for the photopolymer, ULSH-500, under the recording conditions used herein.
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