J. L. Maldonado

Phase stability of guest/host photorefractive polymers studied by light scattering experiments

We report on light scattering measurements in guest/host photorefractive polymers doped with different polar dyes as a function of temperature and sample composition. Crystallization processes of the polar dye are found to follow a nucleation and growth mechanism. The structure and melting point of the polar dye, the storage temperature, and the amount of plasticizer are shown to exert a major influence on the shelf lifetime of the samples. New composites with high efficiency and long shelf lifetime are presented.

Thermally stable high-gain photorefractive polymer composites based on a tri-functional chromophore

We report on the photorefractive properties of thermally stable polymer composites based on the dye 2, N, N-dihexylamino-7-dicyanomethylidenyl-3,4,5,6,10-pentahydronaphthalene. At an applied field of 50 V/μm, we have achieved a dynamic range of Δn=8.5×10−3 and a net two-beam coupling gain of 202u2009cm−1. The diffraction efficiency peaks at an applied field of 28 V/μm, giving an external diffraction efficiency of 71%.

Progress in organic photorefractive material development

The refractive index modulation in photorefractive polymers with a low glass transition temperature is dominated by orientational birefringence effects. To take advantage of these effects we developed several photorefractive polymers that contain: (i) chromophores designed to have simultaneously a large dipole moment and a high linear polarizability anisotropy, (ii) nematic phase liquid crystal droplets, (iii) transparent molecules generally used for liquid crystal applications. We discuss recent advances in these three different classes materials and emphasize their merits and trade-off.

New advances in organic photorefractive material development

The rapid improvement of the performance of photorefractive polymers over the past few years has generated a strong technological interest for these new materials. The areas of application include holographic storage, image processing, optical correlation, and phase conjugation. This paper reviews some of our recent advances in the field of organic photorefractive materials. We will first present several new polymeric composites that combine high efficiency and long shelf lifetimes. Then we will discuss the performance of a new class of organic photorefractive materials: photorefractive polymer dispersed liquid crystals. Finally, we will present two examples of applications based on photorefractive polymers: (i) optical correlators for security verification, and (ii) imaging through scattering media in the near infra-red.

Effect of aryl substitution on the hole mobility of bis-diarylaminobiphenyl-doped polymer composites

Hole mobilities in substituted N, N-bis-(m-tolyl)-N-N-diphenyl-1,1-biphenyl-4,4-diamine (TPD) derivatives doped in polystyrene (PS), were analyzed by the time-of-flight technique to determine the effect of altering the geometric and electronic structure of TPD. Data were collected as a function of applied field and temperature to yield the energetic and positional disorder parameters defined in the disorder formalism. The impact of the molecular dipole moment on transport properties was also evaluated. The larger molecular dipole moments of the derivatives lead to an increase in the energetic disorder, which contributes to their lower mobilities. However, the dipolar disorder contribution was found to account only partially for the large differences in mobility.

Thermally stable high-gain photorefractive polymers based on a trifunctional chromophore

Previously, we have shown that a polymer composite based on polyvinylcarbazole, the dye 2,N,N-dihexylamino-7-dicyanomethylidenyl-3,4,5,6,10-pentahydronaphthalene (DHADC-MPN), the plasticizer N-ethylcarbazole, and the sensitizer (2,4,7-trinitro-9-fluorenylidene)malonitrile (TNFDM) had a real diffraction efficiency of 74% at 830 nm and an externally applied field of 59 V//spl mu/m. This unprecedented performance is the result of the large figure of merit of the chromophore for photorefractivity. In order to improve the thermal stability of these devices, we have developed a stable polymer composite that was prepared by mixing the dye DHADC-MPN with an inert polymer-plasticizer matrix that is more polar than PVK/ECZ. Because the dye acts as a triple-functional dopant, there is no need to incorporate a typically apolar photoconductor that would destabilize the mixture or compete with the dye for free volume. The inert polymer was a birefringence-free acrylic resin composed of poly(methylmethacrylate)-tricyclodecylmethacrylate-N-cyclohexyl maleimidebenzyl methacrylate (PMMA-TMA-CMI-BM). Diphenylisophthalate was used as plasticizer. The results are summarized.

Photorefractive polymer dispersed liquid crystals

Organic photorefractive materials have received increasing attention for photonic applications due to their high performance level and their ease of processing. Here, we preset functionalized polymer dispersed liquid crystals that exhibit strong photorefractive properties. Their properties are investigated by wave-mixing experiments and their performance compared with photorefractive polymers and photorefractive liquid crystals.

High-gain photorefractive polymers

We report on the photorefractive properties of polymer composites based on the dye 2, N, N-dihexylamino-7- dicyanomethylidenyl-3, 4, 5, 6, 10-pentahydronaphthalene (DHADC-MPN). At 633 nm and with 2,4,7-trinitrofluorenone as a sensitizer, the polyvinylcarbazole-based composites show complete internal diffraction at applied electric fields as low as E(pi /2) equals 30 V/micrometer. The sensitivity of the composite could be extended into the infrared by using (2,4,7-trinitro-9-fluorenylidene)malonitrile as a sensitizer, and at 830 nm complete internal diffraction occurred at an applied field of Epi/2 equals 59 V/micrometer. Finally, by using DHADC-MPN as a trifunctional dopant in an inert matrix, we have achieved a dynamic range of (Delta) n equals 0.0085 and a net two-beam coupling gain of (Gamma) equals 202 cm-1 at an applied field of 50 V/micrometer and at 633 nm. The composites are thermally stable or have shelf lifetimes of at least several years at room temperature.