Abstract
Although the angular distribution of noise gratings in holographic photopolymer is understood to arise from Bragg matching, the details of scatter strength and dynamics are not fully understood. This confounds development of materials and recording techniques that minimize haze. Here, the kinetics are studied using a multi-physics numerical approach coupling diffraction of light from the dynamic material including scatter centers, reactions of chemical species initiated by this light, diffusion and swelling of these constituents, and the formation of the refractive index from the resulting composition. The approach is validated in the case of two-beam transmission holography by comparison to traditional harmonic series and rigorous coupled-mode approaches. Two beam holography in the presence of scatter is then used to study haze development. This reveals that haze due to weak noise gratings grows significantly above initial scatter only in reaction-limited materials, consistent with proposed Bragg-matched amplification mechanisms. Amplified haze is found to be proportional to initial scatter, quantifying the impact of clean sample fabrication. Conversely, haze is found to grow super-linearly with sample thickness, illustrating the significant challenge for applications requiring low haze in large thickness.
Highlights
Most applications of holographic photopolymers require high diffraction efficiency and low scatter
The validated code is applied to investigate how noise and signal develop in a holographic photopolymer containing scatter centers
The holographic photopolymer uses bisphenol A diacrylate (BPADA) as a writing monomer in a polyurethane matrix initiated with 2,4,6-trimethylbenzoyl (BPADA) as a writing monomer in a polyurethane matrix initiated with 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) at 405 nm
Summary
Most applications of holographic photopolymers require high diffraction efficiency and low scatter. Examples include data storage, where scatter contributes to the bit error rate, and augmented reality where scatter contributes to haze that detracts from visibility It is commonly observed in material development that these two quantities are coupled. The central concept of these studies is that recorded scatter must be considered as an ensemble of weak holograms, a small fraction of which are Bragg-selectively replayed by the reference and object beams. This amplifies a fraction of the scatter which interferes with the writing beams to write further noise gratings
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