Recent research on an acrylamide-based photopolymerizable holographic recording material is presented. The recording characteristics of the material are discussed in detail in terms of sensitivity, diffraction efficiency, recording linearity, resolution limit, and sources of noise. Although the resolution is not sufficient for reflection holography, the recording characteristics are excellent for transmission gratings. The material was found to suffer no shrinkage during recording, and high-diffraction-efficiency slanted gratings were made. Finally, the suitability of this self-developing material to both double-exposure and real-time holographic interferometry is demonstrated.

A reflection hologram for visual indication of environmental humidity has been studied. The hologram is recorded in a self-developing photopolymer and changes color when exposed to a change in humidity and is fully reversible. The range of color change, reversibility, and the response time of the hologram have been studied in a controlled humidity environment. Fully reversible holograms with response times from few seconds to tens of minutes have been designed. Extremely sensitive bright visual humidity indicators, capable of dramatic color change within a few seconds of breathing on them are demonstrated.

Results from the investigation of the diffusion processes in a dry acrylamide-based photopolymer system are presented. The investigation is carried out in the context of experimental research on optimization of the high-spatial-frequency response of the photopolymer. Tracing the transmission holographic grating dynamics at short times of exposure is utilized to measure diffusion coefficients. The results reveal that two different diffusion processes contribute with opposite sign to the refractive-index modulation responsible for the diffraction grating buildup. Monomer diffusion from dark to bright fringe areas increases the refractive-index modulation. It is characterized with diffusion constant D ₀ = 1.6 × 10^-7 cm²/s. A second diffusion process takes place during the recording. It decreases the refractive-index modulation and we ascribe it to diffusion of short-chain polymer molecules or radicals from bright to dark fringe areas. The estimated diffusion coefficient for this process is D ₀ = 6.35 × 10^-10 cm²/s. The presence of the second process could be responsible for the poor high-spatial-frequency response of the investigated photopolymer system. Comparison with the diffusion in photopolymer systems known for their good response at high spatial frequencies shows that both investigated diffusion processes occur in a much faster time scale.

Recent work on an acrylamide-based photopolymer holographic recording medium is presented. The lifetime of recorded gratings is improved by the addition of cross-linking monomers. Shelf life is also improved. The effects of various constituents of the photosensitive material are studied to determine an optimum composition, and five xanthene dyes are compared as possible sensitizers for the system. With the most sensitive dye and optimum concentrations of the other constituents an improved formulation is presented with high sensitivity and very high diffraction efficiency. The new formulation also works well in reflection mode.

A holographic device is under development that aims to improve light collection in solar cells. The aim is to explore the potential of using photopolymer holographic optical elements (HOEs) to collect light from a moving source, such as the sun, and redirect it for concentration by a holographic lens. A working range of 45° is targeted for such a device to be useful in solar applications without tracking. A photopolymer HOE is capable of efficiently redirecting light, but the angular selectivity of a single grating is usually of the order of one degree at the thicknesses required for high efficiency. The challenge here is to increase the angular and wavelength range of the gratings so that a reasonable number may be multiplexed and/or combined to create a device that can concentrate light incident from a large range of angles. In this paper, low spatial frequency holographic recording is explored to increase the angular and wavelength range of an individual grating. Ultimately, a combination of gratings will be used so that a broad range of angles of incidence are accepted. A design is proposed for the combination of such elements into a holographic solar collector. The first step in achieving this is optimization of recording at low spatial frequency. This requires a photopolymer material with unique properties, such as a fast monomer diffusion rate. This paper reports results on the efficiency of holograms recorded in an acrylamide-based photopolymer at low spatial frequencies (100, 200, and $300\mathrm{l}/\mathrm{mm}$). The diffraction efficiency and angular selectivity of recorded holograms have been studied for various photopolymer layer thicknesses and different intensities of the recording beams. A diffraction efficiency of over 80% was achieved at a spatial frequency of $200\mathrm{l}/\mathrm{mm}$. The optimum intensity of recording at this spatial frequency was found to be $1\mathrm{mW}/{\mathrm{cm}}^2$. Individual gratings and focusing elements with high efficiency and FWHM angles of 3° are experimentally demonstrated.