Photorefractive polymers responses

Photorefractive Polymers Polymers that are used to write and read information through their characteristics of charge, motion and nonlinear optical response. 

Table 1. Rate of response of selected photorefractive polymer composites a comparison of the experimental fast time constant of growth of contrast in refractive index in response to a nonuniform intensity pattern and the theoretical rate limit based on charge photogeneration rate.

Other applications that were recently demonstrated with photorefractive polymers include homodyne detection of ultrasonic surface displacements using two-wave mixing [115]. With the development of new photorefractive polymers with response times in the millisecond range, numerous optical processing techniques can be performed at video rates. Image amplification and novelty filtering at video rates were demonstrated recently [116]. All-optical processing techniques compete with computational methods. Therefore, it is important that photorefractive polymers exhibit faster response times in the future. 

The following seems to be a general rule The response times of photorefractive polymer composites are strongly dependent on both the glass transition temperature and the electro-optical chromophore. ... 

N. (2006) Photorefractive Polymers with Sub-millisecond Response Time, vol. 6335, SPIE, p. 633503. 

Peyghambarian, N., and Yamamoto, M. (2006) Photorefractive polymer device with video-rate response time operating at low voltages. Opt. Lett., 31 (10), 1408-1410. 

While polymeric photorefractive materials can be prepared by adding separate molecules for photo-generation, charge transport and non-linear optical response into an inert polymer, most systems studied use polymers where one or more of these components are covalently bonded to the polymer. Polymer... 

The field of photorefractivity in organic polymers and glasses has been in existence for less than a decade. The understanding of charge generation in these materials (which are often composites) is not yet mature, and the behavior of some of the more common constituents is understood better. Much of the literature on photo-refraetivity deseribes free earrier generation quantum efficiency measurements only briefly, before a more detailed discussion of other factors such as mobility and electro-optic response. Some of the relevant information pertinent to free carrier generation in these materials is presented here, to be followed by a review of this aspect of the amorphous photorefractives literature. 

If bifimctional molecules do not form glasses, they can be incorporated into polymer binders. Examples of bifunctional molecules are shown in Fig. 24. DTNBl (molecule (b) in Fig. 24) was doped in PMMA and Cgg was used as a sensitizer. Diffraction efficiencies of 7%, sub-second grating growth times, and net two-beam coupling gain coefficients of 34 cm" were observed in such samples [81]. DPANST (molecule (c) in Fig. 24) was doped into PBMA [84]. Recently, ms response times were reported in photorefractive glasses based on the bifunctional chromophore DRDCTA (molecule (d) in Fig. 24) doped with the plasticizer DOP (molecule (b) in Fig. 23) and Cgg as a sensitizer [89, 90]. 

I)i94 i94a were investigated as photorefractive materials. Substantial photorefractive responses were measured in both doped and undoped samples, as pure materials and as materials dispersed within polymers. 

A polymer composite of PVK/TNF, doped with DMNPAA can still be improved by modifying the structure of DMNPAA. DMNPAAs modified with certain alkyl substituents have fast orientational response to an external electric field and keep large anisotropy in polarizability. 4-But-oxy-3-propyl-l-(4 -nitrophenylazo)benzene has the shortest reorientation time constant of 19 ms and photorefractive time, which are 2,300 times and 63 times faster than those of a simple DMNPAA composite. The fast reorientational response results from the improvement of the dispersivity in the polymer composites and the decrease of the glass transition temperature. 

Poly(siloxane)s. An alternative to PVK is the hole-transporting polymer poly(methyl-bis-(3-methox5 henyl)-(4-propylphenyl)amine)siloxane. It has been doped with the photorefractive chromophore 4-di(2-methoxy-ethyl) aminobenzylidene malononitrile. The low intrinsic glass transition temperature of the siloxane pol5mier allows the preparation of samples without additional plasticizers. The composites exhibit good chromophore orientational mobility and exhibit photorefractive response times in the millisecond range. ... 

Fast response photorefractive materials that are based on abis-triarylamine side-chain polymer matrix with a low ionization potential [171] have been described. 

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