In this work we analyze the optical quality, performance, and recording mechanism of holographic diffraction gratings
recorded in photopolymerizable sol-gel glasses. These classes of holographic photomaterials have various compositions,
one of which incorporates a High Refractive Index Species (HRIS), already developed in our group GICO-UCM. The
new types of photopolymerizable glasses under study incorporate ionic liquid (IL). We present a comparative study,
showing distinctive behaviors for each photopolymerizable glass class, and determining particular features for various
ranges of applications.
We report recent results obtained with volume holographic gratings recorded in a new photopolymerisable glass
modified with high refractive index species at molecular level. Various not previously observed performances have been
achieved for diffraction efficiency and angular selectivity. In particular, new overmodulation effects have been observed
for the first time experimentally in an amorphous material.
A photoconductive sol-gel material based on the incorporation of polyvinyl carbazole (PVK) and 2,4,7-trinitro-9-fluorenone (TNF) within a silica matrix is reported. Unmatched photosensitive as large as 10-10 cm/ΩW has been found at moderate applied electric fields (20 V/μm). The optimization of the concentration balance between the functional component (the TNF/PVK molar ratio percent) has resulted in a 300-fold increase of the photocurrent efficiency (Φ). The study of photcoductivity of sol-gel materials prepared with different PVK contents has confirmed the unneeded use of massive photoconductive materials to obtain optimum performance.
A holographic hybrid sol-gel material with excellent values of diffraction efficiency, index modulation and high photosensitivity (up to 93%, 10-3, and 5 x 10-3 cm2/mJ, respectively) is reported. Moroever, a high angular selectivity has been achieved $9 = 0.0967°) through the selection of the adequate nanoporous silica supporting matrix. Such a value has allowed to first demonstrate the capability of angular multiplexing in a holographic sol-gel media (up to five volume holograms with a resultant M/# of 0.83 in a preliminary approach). Shrinkage during UV curing processes has also been determined in order to evaluate how accurate can be the retrieval of the recorded data.
This work describes how the sol-gel process can be a useful approach for the preparation of hybrid materials showing either holographic as well as photorefractive properties. The composition of the holographic and photorefractive materials prepared through the sol-gel approach are completely based on their respective multi-functional polymer analogues, but in the polymer acting as host matrix which is replaced by a nanoporous silica matrix. Such a replacement infers an overall improvement in both the optical and the mechanical properties of the material. The goodness of the properties found for either the holographic as well as the photorefractive materials demonstrate the validity of these new synthetic routes for the preparation of optical recording materials.
Two novel holographic recording media based on silica gel methyl methacrylate (MMA) and hydroxy ethyl methacrylate (HEMA) organically modified ceramics (ORMOCERS) are presented and its holographic properties, inferred from the experimental data, are discussed. The recording of holographic gratings of both low-spatial frequency (50 lp/mm) and high-spatial frequency (1400 lp/mm) in a bulk ORMOCER matrix is reported. The gratings were recorded by UV irradiation-induced photopolymerization of the MMA or HEMA monomers embedded in the silica matrix. The Bragg gratings were successfully recorded by interference of two coherent beams of 351.1 nm wavelength. A linearly polarized He-Ne laser beam (632.8 nm) was used for continuous monitoring of the recording process by measurement of the diffraction efficiency and for enhancement of the grating creation process. High diffraction efficiencies (93%) and low absorption and scattering coefficients were measured during the holographic reconstruction by He-Ne laser beam. The most important holographic parameters of the gratings were inferred from the experimental data: diffraction efficiency, angular selectivity, refraction-index modulation amplitude, spectral sensitivity, the Klein-Cook parameter, and the environmental stability of the gratings.
Several dyes such as a spiropyran, a spirooxazine and two tetraarylporphyrins have been incorporated inside hybrid organic-inorganic matrices synthesized through the acid hydrolysis of dimethyldiethoxysilane and zirconium n- propoxide. These matrices are nanocomposites with well defined hydrophilic (zirconium oxopolymer nodules) and hydrophobic (polydimethylsiloxane chains) domains. As a consequence, they are good candidates to investigate dye-matrix interactions in matrices containing transition metal. These interactions are shown to occur through hydrogen bonds, covalent bonds or Lewis acid-base type bonds. They strongly modify the optical response of the dyes (absorption-emission spectra, lifetime, kinetics...).
Variable delays in fiber optic optical transmission have been achieved by using photochromic- doped sol-gel silica glasses. Gaps between two commercial fibers in V-groove connectors, when filled with these materials, produce variable propagation times. Variations of the optical propagation time depending on the input power, wavelength, and dopant concentration are shown.
The lifetime of the near-infrared emission of oxazine-1 and 1,1',3,3,3',3'- hexamethylindotrycarbocyanine iodide (HITC) into gel-glasses prepared from TMOS or TEOS are studied by variable frequency phase and modulation data. Analysis of the lifetime by a fitting procedure to an assumed model revealed two lifetimes with a low value of the reduced chi-squared for the studied doped gel-glasses. The longer lifetime is attributed to the adsorbed species, while the shorter to species which are affected by the remaining solvent in the pores. The contributions of these species to the total fluroescence are also resolved.
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