Characteristics of DuPont photopolymers for slanted holographic grating formations

The characteristic parameters of DuPont OmniDex613 photopolymers including the shrinkage factor, diffusion coefficient, and nonlocal response length are studied for slanted holographic gratings recorded at the UV wavelength of 363.8 nm by application of the rigorous coupled-wave analysis in conjunction with an angular-selectivity measurement, a real-time diffraction-monitoring technique, and a nonlocal diffusion model. Both small (<20 deg) and large (>40 deg) slant-angle gratings are presented. Depending on the exposure intensity, the recording shrinkage factor of the photopolymer varies from ~2.75% to ~4.20%. Furthermore, the effects of postbaking conditions on the refractive-index modulations and the shifts of Bragg angles for slanted holographic gratings are also investigated systematically. It is found that the postbaking processing can not only increase the refractive-index modulations from Δn1~0.013 to ~0.028 for a small slant-angle grating and from Δn1~0.011 to ~0.022 for a large slant-angle grating, but can also compensate the recording shrinkage.