Optical and holographic characteristics of photopolymer layers

The present work studies the optical and holographic characteristics of acrylamide-based photopolymer layers. The refractive index change of a liquid acrylamide photopolymer due to exposure at 532 nm is obtained for the first time, using a critical angle laser micro-refractometer. The 30 μm thick solid photopolymer films are prepared by casting on glass substrates. Bragg holographic gratings with spatial frequencies of 710 mm^-1, 1050 mm^-1 and 1600 mm^-1 are recorded using a diode laser operating at 532 nm wavelength. We investigate the dependence of the diffraction efficiency on the exposure energy. The obtained results are compared with the Stetson holographic recording method, where two gratings are simultaneously recorded in the same location with spatial frequencies of 2020 mm^-1 and 3670 mm^-1, using a totally reflected reference wave from the air-photopolymer interface. Despite the fact that in the latter method the two gratings share the same dynamic range, higher diffraction efficiencies are observed.