Photorefraction polymer composition

Mecher, E., Gallego-Gomez, F., Tillmann, H., Horhold, H.H., Hummelen, J.C., and Meerholz, K. (2002) Near-infrared sensitivity enhancement of photorefractive polymer composites by pre-illumination. 

Figure 10. Top liquid-phase absorbance spectrum of each component of a typical photorefractive polymer composite. Each component, A -vinylcarbazole (PVK), 2,4,7-trinitro-9-fluorenone (TNF), and typical chromophore (EHDNPB), is diluted in dichloromethane separately. (Absorption due to the solvent has been subtracted.) Bottom the absorbance of light in a solid sample due to the charge transfer complexation between PVK and TNF. The sample was prepared from a 9 1 ratio of PVK/ TNF. The extension of absorption to longer wavelengths is clear.

Figure 11. Possible relative positions of the energy levels in a typical guest-host photorefractive polymer composite containing PVK, TNF, and an azo-chromophore. A possible sequence of events leading to mobile charge generation is also included.

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.

Figure 16. Transient photocurrent signal from a time-of-flight measurement of a photorefractive polymer composite containing 47.5 % electro-optic dye (EHDNPB), 1 % TNF with PVK polymer making up the remainder 21 V was applied across the 100 nm polymer film and a 10 nm thick rhodamine 6G charge generation layer was used. The hole mobility in this material is thus...

Figure 19. A typical HTOF signal from the photorefractive polymer composite PVK/0.1 wt.% TNF and 40 wt.% 4-(hexyloxy)nitrobenzene electro-optic chromophore, reproduced with permission from [42]. A clear peak is observed which represents the transit time of holes across half a grating period. Eventually a steady state is reached due to the spatial hole distribution being smeared out by dispersive transport and hole recombination.

In the photorefractive polymer composites described above, the value of the glass transition temperature is of great importance because it needs to be in a range where the electro-active chromophores can be reoriented by the photorefractive space-charge charge field. Adjustment of Tg is done though the addition of a plasticizer. Examples of plasticizers are shown in Fig. 23. As for the polymer matrixes, plasticizers can be photoconducting or inert. ECZ (molecule (a) in Fig. 23) is widely used with PVK. Inert plasticizers such as BBP (molecule (c) in Fig. 23) have also been combined with PVK [86]. 

Fig. 27. Field dependence of the two-beam coupling gain measured in the photorefractive polymer composite PDCST PVK BBP C5o squares single sample (140 pm-thick) circles a two-layer stack triangles a three-layer stack... 

Colloidal Gold. A photorefractive polymer composite composed from PVK, TNF, 4-(dicyanovinyl-A,A-diethylaniline), and gold particles, exhibited an effective enhancement on the photorefractivity. " It is suggested that the enhancement on the photorefractivity is due to the increment of the density of the effective trap center by doping with gold particles. 

Full-held, retrorehective holographic imaging through turbid media has been achieved using a photorefractive polymer composite as a coherence gate The photorefractive devices used, are based on PVK and TNFDM which is doped with the chromophore l-(2 -ethylhexyloxy)-2,5-dimethyl-4-(4 -nitrophenylazo)benzene. There is certain evidence that TNFDM interacts with chromophores by complexation. ... 

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. ... 

D. Wright, U. Gubler, Y. Roh, W. E. Moemer, M. He, and R. J. Twieg. High-performance photorefractive polymer composite with 2-dicyano-methylen-3-cyano-2,5-dihydrofuran chromophore. Appl. Phys. Lett., 79 (26) 4274 276, December 2001. 

E. J. Smiley, D. J. McGee, C. Salter, and C. R. Carlen. Diffraction efficiency and phase stability of poly(V-vinylcarbazole)-based photorefractive polymer composites as a function of azo-dye concentration. 7. Appl. Phys., 88(8) 4910-4912, October 2000. 

P. Dean, M. R. Dickinson, and D. P. West. Full-field coherence-gated holographic imaging through scattering media using a photorefractive polymer composite device. App/. Phys. Lett., 85(3) 363-365, July 2004. 

E. Hendrickx, Y. D. Zhang, K. B. Ferrio, J. A. Herlocker, J. Anderson, N. R. Armstrong, E. A. Mash, A. P. Persoons, N. Peyghambarian, and B. Kip-pelen. Photoconductive properties of PVK-based photorefractive polymer composites doped with fluorinated styrene chromophores. J. Mater. Chem., 9(9) 2251-2258, September 1999. 

For several decades, the fields of photoconducting (75) and purely electrooptic polymers (74) have been very active but had almost no direct overlap. With the development of photorefractive polymers in the early nineties, the knowledge of these two research areas could be combined and has led to a rapid improvement of the performance of existing photorefractive polymers. The photorefractive polymer composite DMNPAA PVK ECZ TNF (DMNPAA 2,5 -dimethyl-4-(p-nitrophenyl-azo)anisole PVK poly(N-vinylcarbazole) ECZ N-ethylcarbazole TNF 2,4,7-trinitrofluorenone) we developed recently (P) has reached a level of performance that competes with that of the best inorganic photorefractive crystals (77,72). With the recent progress achieved in the development of new chromophores for electro-optic applications (75), the efficiency of these new materials is expected to be significantly further improved. 

For testing, an object image produced by a computer was displayed on a spatial hght modulator and used for the hologram. The reflected object beam from a spatial hght modulator was interfered with a reference beam on the photorefractive polymer composite to record a hologram. 

Full-field, retroreflective holographic imaging through turbid media has been achieved using a photorefractive polymer composite as a coherence gate [182], The photorefractive devices used, are... 

Tsutsumi N, Kinashi K, Nonomura A, Sakai W. Quickly updatable hologram images using poly(A-vinyl carbazole) (PVCz) photorefractive polymer composite. Materials 2012 5(12) 1477-86. 

Wright D, Gubler U, Roh Y, Moerner WE, He M, Twieg RJ. High-performance photorefractive polymer composite with 2-dicyanome-thylen-3-cyano-2,5-dihydrofuran chromoph-ore. Appl Phys Lett 2001 79(26) 4274-6. 

Hendrickx E, Zhang YD, Ferrio KB, Herlocker JA, Anderson J, Armstrong NR, et al. Photo-conductive properties of PVK-based photorefractive polymer composites doped with fluo-rinated styrene chromophores. J Mater Chem 1999 9(9) 2251-8. 

It was pointed out that the performance of photorefractive polymer composites is too large to be explained by the simple electrooptic photorefractive effect alone. A theoretical model was offered where both the birefringence and electrooptic coefficient are periodically modulated by the space-charge field due to the orientational mobility of the nonlinear chromophores at ambient temperatures. 

Figure 6. Intensity of the scattered light as a function of time for a photorefractive polymer composite of DMNPAA PVK CZ with composition 39 41 20 wt. % held at 55< C.

A number of composite systems have been reported in which a polymer possessing one of the requisite functionalities, e.g., covalently attached NLO chromophores, is doped with the others, e.g., CG and CT dopants, or a photoconductive polymer, e.g., poly(N-vinylcarbazole), is doped with the sensitizer and NLO dopants (1, 4-7). The high dopant loading levels necessary (up to 50 wt%) result in severe limitations of doped systems, including diffusion, volatilization, and/or phase separation (crystallization) of the dopants. In addition, plasticizers and compatibilizers are often used to lower the glass transition temperature (Tg) of the polymer and increase solubility of the dopants in the host polymer, respectively. This, in turn, dilutes the effective concentration of CT, CG, and NLO moieties, diminishing the efficiency and sensitivity of the photorefractive polymer composite. 

F., and Sastre-Santos, A. (2009) Ph-thalocyanines as efEcient sensitizers in low-Tg hole-conducting photorefractive polymer composites. Chem. Mater., 21, 2714-2720. 

Choi, C.S., Moon, I.K., and Kim, N. (2009) New photorefractive polymer composites doped with liquid nonlinear optical chromophores. Macromol. Res.,... 

West, D., Rahn, M., Im, C., and Bassler, H. (2000) Hole transport through chromophores in a photorefractive polymer composite based on poly(N-vinylcarbazole). Chem. Phys. Lett., 326, 407-412. 

Casperson, ).D., DeGlue, M., Moerner, W.E., and Twieg, R.]. (1998) High-speed photorefractive polymer composites. 

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