Holographic multiplexing in a photorefractive polymer

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.