Improving performance oftwo‐stagephotopolymers for volume holographic recording by fluorinatedepoxy‐amine cross‐linkedmatrices

Abstract

Host matrices play an important role in the volume holographic gratings formation of photopolymers. In this study, a series of fluorinated epoxy resin (FTGE) with low refractive index (1.44-1.46) are synthesized and characterized by nuclear magnetic resonance spectra ( 1 H NMR, 19 F NMR) and fourier transform infrared spectra (FTIR). Fluorinated epoxy-amine cross-linked matrices are formed at room temperature and their thermal polymerization properties are investigated through real-time FTIR and thermogravimetric analyses (TGA). Using the fluorinated epoxy-amine as host matrices, holographic photopolymers are fabricated. The influence of different kinds (Prop-FTGE, Buta-FTGE, and Penta-FTGE) and weight ratios (0%, 8%, 16%, and 23%) of FTGEs on holographic performances of the photopolymers are explored. The results show that the sample with 23% Prop-FTGE has the most excellent holographic optical characteristics. 0.5 mm thick sample with 23% Prop-FTGE reaches 91% diffraction efficiency within 80 mJ/cm 2 exposure dosage, and gets a 2000 lp/ mm Bragg volume grating with 0.24 angular selectivity. Meanwhile, under a single pulse exposure mode (150-200 ps pulse width, 25 mJ/cm 2 exposure dosage), a grating with 4.4% diffraction efficiency is obtained, which proves the ultrafast response and recording capability of the sample.

High Refractive Index Monomers for Improving the Holographic Recording Performance of Two-Stage Photopolymers

“…The sensitivity ( S ) of the samples was calculated according to eq . The Δ n of a VHG was calculated according to eqs –. η = I normald I normald + I normalt 100 % where I d and I t are the intensities of diffracted beam and transmitted beam; S = η max I t = η max E where I is the exposure intensity, t is the exposure time, and E is exposure dosage in η max …”

“…Generally, a photopolymer formulation for recording a VHG consists of three main components: photoinitiating system (including photoinitiator and/or photosensitizer), writing monomers, and host matrice (binder or film-forming resin) . In a two-stage photopolymer, first, a cross-linked host matrix is formed to provide a physical scaffold before exposure, in which monomers can diffuse and migrate.…”

“…Furthermore, they selected a more suitable photoinitiating system and achieved a VHG with 0.045 of Δ n . Meanwhile, it was widely reported that the holographic recording performance of a photopolymer could be improved significantly by using resins containing fluorine or silicon with lower refractive index as matrices. ,, Therefore, many new monomers with higher refractive index have been developed. − Lee et al synthesized a new monomer DT ( n = 1.617) and produced a VHG with a diffraction efficiency of 98% using photopolymer with DT added . Hawker et al synthesized four dendrimers with high refractive index (1.614–1.663) and got a VHG with a reduced shrinkage of 0.03% using photopolymer containing these dendrimers …”

“…16 Meanwhile, it was widely reported that the holographic recording performance of a photopolymer could be improved significantly by using resins containing fluorine or silicon with lower refractive index as matrices. 17,22,23 Therefore, many new monomers with higher refractive index have been developed. 24 1.663) and got a VHG with a reduced shrinkage of 0.03% using photopolymer containing these dendrimers.…”

“…Generally, a photopolymer formulation for recording a VHG consists of three main components: photoinitiating system (including photoinitiator and/or photosensitizer), writing monomers, and host matrice (binder or film-forming resin). 17 In a two-stage photopolymer, first, a cross-linked host matrix is formed to provide a physical scaffold before exposure, in which monomers can diffuse and migrate. Second, under the irradiation of two coherent laser beams, the photoinitiating system in the coherent bright fringes initiate the polymerization of the monomers, 18−20 resulting in a concentration difference of monomers between bright and dark fringes, so that the monomers will tend to migrate from dark fringes to bright fringes to participate in the polymer-ization.…”