Organic photorefractive materials

About: Organic photorefractive materials is a research topic. Over the lifetime, 697 publications have been published within this topic receiving 13041 citations.

Holographic multiplexing in a photorefractive polymer

Abstract: Summary form only given. With the advent of the orientational enhancement effect, photorefractive polymer materials have undergone tremendous improvements in their performance as measured by the maximum achievable refractive index modulation and two-beam coupling gain. However, measurements concerning these material's ability to record multiple overlapping holograms have not been performed. In order to be useful for holographic data storage applications, a material must be capable of achieving a high M/#, a property dependent on both the recording and erasure dynamics of the stored holograms. With conventional inorganic photorefractive materials, mono-exponential recording and erasure dynamics are observed, allowing the M/ to be calculated by measuring the initial slope of the recording curve and the single hologram erasure time constant. Using a photorefractive polymer consisting; of (by weight) 42% poly-(N-vinylcarbazole) (PVK), 7% N-ethylcarbazole (ECZ), 25% each of the nonlinear chromophores 2,5-dimethyl-4,4'nitrophenylazoanisole (DMNPAA) and 2-methoxy-4,4'-nitrophenylazoanisole (MNPAA), and 1% 2,4,7-trinitrofluorenone (TNF), we measured the recording and nonBragg matched erasure dynamics. In order to record multiple holograms of equal strength, a suitable exposure schedule must be devised. The experimentally measured erasure curves can be fit by a series of decaying exponentials. The recording time required for each hologram can then be computed by numerically solving the set of fit exponential series for the necessary hologram strength.

Nonlinear light-induced absorption in Bi_2TeO_5 photorefractive crystals

Abstract: We report on the light-induced absorption in undoped photorefractive Bi2TeO5 (BTeO) crystal. The so-called “two-center” model is shown to adequately describe the present material behavior. We demonstrate that nonlinear light-induced absorption occurs for high light intensities. The theoretical model allowed us to find out some material parameters from experimental data. We also investigate the effect of intensity and wavelength on the light-induced absorption.

Temperature dependent measurements on a low-molecular-weight photorefractive glass

Abstract: The erasing dynamics of holographic gratings in a low molecular weight photorefractive glass depending on thesample temperature were investigated. Changes in the overall speed of the material by three orders of magnitudeover a temperature range of 13 K were observed. We identified two distinct processes below the glass transitiontemperature Tg , a fast one on time scales of seconds and a slower one with lifetimes around iO s. We attributethe fast process to the electrooptic effect and the slower one to orientational diffusion processes of the glass molecules. Above Tg , the fast process vanishes, whereas the diffusional processes accelerate up to time constantsin the range of seconds. This study shows, that an accurate temperature control is indispensable when measuringphotorefractive dynamics, especially in the temperature range around Tg. 1. INTRODUCTION Since the discovery of the photorefractive effect in an organic polymer in 1990,1 amorphous organic photorefrac-tive materials are considered to be very promising for holographic applications because of their low cost, easysynthesis, and straightforward processing. The photorefractive effect is characterized by a non-local variationof the refractive index of the material due to inhomogeneous illumination. Two interfering laser beams createan intensity grating in the photorefractive sample. Charge carrier separation occurs in the bright regions; asthe result of different charge carrier mobilities, one kind of carriers, in organic materials usually the electrons,stays in place while the more mobile holes move to darker areas, where they become trapped. This yields aninhomogeneous charge density respectively a space charge field E8, which modulates the externally applied dc

Photorefractive Effect Due To Holes In Undoped BGO Crystals

Abstract: The investigation of the photorefractive properties in various sillenite crystals (Bil2Si020 - Bil2Ge020) is presented. While in some crystals we find a photorefractive effect governed by electron migration as commonly admitted, we, for the first time, demonstrate that holes play the most important role in the grating recording process in some EGO samples. Thus controlling the charge carrier responsible for the photorefractive effect might lead to an optimisation of the material properties for device design.© (1987) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.