A polymeric holographic material with diffusion amplification for the near-UV region

Abstract

This paper presents the results of experimental studies of the optical recording and thermal amplification of phase gratings in a new polymeric composite with diffusion amplification, based on PMMA and benzophenone. The phase gratings were recorded by exposing layers to incoherent UV radiation (365 nm) through an amplitude mask and an interference pattern formed by the radiation of a pulsed Nd : YAG laser (355 nm). Post-exposure heat treatment of the layers resulted in amplification of the gratings. The kinetics of the process are consistent with concepts of the diffusion nature of the amplification. The photo-and thermostability of the gratings after amplification made it possible to conclude that photoattachment of the benzophenone to the PMMA occurs in the layers, resulting in diffusion relaxation of the inhomogeneous distribution of the benzophenone concentration. Refractive-index modulation of 1.6 × 10 −3 was achieved for PMMA layers containing benzophenone with a mole fraction of 2%.Polymeric holographic materials with diffusion amplification, which allow layers to be deposited from solution and stored for a long time before recording, make it possible to obtain volume holograms with maximum diffraction efficiency and high radiation strength with no liquid development. 1 These advantages are essential for applications in production technologies-for example, in UV photolithography using holographic photomasks. 2 The recording and functioning of the latter in the UV region requires holographic materials that are sensitive to UV radiation and requires the amplified and fixed holograms to have the maximum transparency and stability. Known phenanthrenequinone-based holographic materials provide efficient volume recording in the blue-green region, and the possibility of reconstruction is limited to the region ≈400 nm. The shorter-wavelength radiation in absorbed by the photoproducts of the phenanthrenequinone. In this connection, it is crucial to search for new photosensitive compounds with optical absorption in the UV region and photochemical properties similar to those of phenanthrenequinone. This paper discusses a polymeric composite that includes photosensitive additive benzophenone (BP), whose main photoreaction in polymethyl methacrylate (PMMA), as for phenanthrenequinone, is photoreconstruction. EXPERIMENTLayers of PMMA with thickness within the limits 1-100 µm and 1-7% mole fraction of BF were used for this work. Thin layers (up to 5 µm) were prepared by centrifugation, and thicker layers by pouring a solution of the ingredients onto a glass substrate, followed by drying.The electronic absorption spectra of the layers were measured by means of a Specord M40 spectrophotometer. Nonsinusoidal thin transmitting phase gratings (NPGs) were formed in layers 20-40 µm thick by exposure through a mask that creates a periodic intensity distribution in the layer (d = 9-30 µm). The 365-nm line of a DRSh-250-3 mercury lamp, isolated by a filter, was used as activating radiation. The holographic recording was carried ou...

Dye-doped PQ-PMMA phase holographic materials for DFB lasing

“…Spectral selectivity of about several angstroms was also achieved for diffractive optical filters based on thick reflective gratings [9]. Current investigations of holographic PMMA-PQ photopolymers stimulated the recent development of new materials, based on the diffusion amplification mechanism due to photoinduced grafting, sensitive in the UV [12][13][14] or in the vis range [15] of the spectrum.…”