Effect of Monomers on the Holographic Properties of Poly(vinyl alcohol)-Based Photopolymers

Abstract

Based on the poly(vinyl alcohol) (PVA) system, photopolymers were prepared with two different monomers: Nvinylpyrrolidone (NVP) and acrylamide (AM). The maximum diffraction efficiency of the photopolymers was more than 85%, and the maximum sensitivity was 17.77 × 10 −3 cm 2 /mJ. The optimized photopolymer with high diffraction efficiency and high photosensitivity can achieve both the recording and reproduction of reflection holography and the recording and reproduction of transmission holography. At the same time, the effects of monomer on holographic properties of photopolymers were studied. It was found that the reactivity and migration rate of the monomer worked together on the polymerization rate, which affected the holographic properties of the photopolymer. To verify the influence of the structure of NVP and AM on the reactivity and migration rate, the transmittance and the real-time diffraction efficiency measurements were innovatively used. The NVP with high electron cloud density was more reactive, while the AM with low molecular weight and simple molecular structure had a faster migration rate.

Effect of Glycerol on an N-Vinylpyrrolidone-Based Photopolymer for Transmission Holography

“…According to the peak intensity of the , a curve of the conversion rate of NVP over time can be obtained. The monomer conversion rate is calculated as shown in Equation (5) [ 16 ]: where represents the intensity of the when the exposure time is t .…”

“…The image produced by a hologram has the advantage of a 3D effect and realistic depth perception. Holography mainly has two recording methods, reflective and transmissive [ 16 , 17 ]. Transmission holography is the main method to obtain holograms of large scenes, so it has greater application prospects.…”

“…When NVP is used in a polyvinyl alcohol system, the saturation refractive index modulation reaches 1.2 × 10 −2 , which makes it an excellent candidate for preparing photopolymers with high refractive index modulation. However, NVP has a five-membered ring substituent, and its molecular weight is much larger than that of acrylamide [ 16 , 18 ], which makes the diffusion of NVP slow during the holographic recording process. This is not conducive to the realization of holographic recording, especially long-distance diffusion holographic recording at low spatial frequency.…”

“…In other words, to obtain high-quality transmissive holograms, photopolymer materials are required to have excellent holographic performance at lower spatial frequencies. As a common polymerizable 2 of 12 monomer, NVP has been successfully used in the preparation of water-soluble polyvinyl alcohol system photopolymers [16]. NVP has a high refractive index (n = 1.512).…”