Photorefractive polymer-dispersed liquid

To overcome volatility problems, two-photon absorption (TPA) is the most promising long-term data storage technique to date. TPA can be observed in all materials and lacks the noncentrosymmetric symmetry requirements of even-order nonlinear optical effects. Nevertheless, in centrosymmetric polymers two-photon absorption is allowed between states that have the same parity according to parity selection rules (112). Such a system has been demonstrated with nondestructive readout (113). Additionally, use of two-photon absorption on photorefractive polymer dispersed liquid crystals has been used to record a high 3D data density of 204.8 Gbits/cm (158). 

Figure 10. Design principle of photorefractive polymer-dispersed liquid crystals.

Holographic optical elements can also be made by the preparation of polymer-dispersed liquid crystals using twin lasers in transmission holographic photopolymerisation (see section 5.4.2). They have also been made using photorefractive composites of polymer dispersed liquid crystals (see section 5.6.3). 

Fig.25. Normalized diffraction efficiency vs applied field measured in 105 pm-thick samples of the polymer-dispersed liquid crystal TL202 PMMA ECZ TNFDM (circles) and the photorefractive polymer DHADC-MPN PVK ECZ TNF (squares)...

Photorefractive Polymers and Polymer-Dispersed Liquid Crystals... 

Inorganic organic hybrid polymer dispersed liquid crystalline nanocomposites are reported as suitable candidate for fahricatirHi of photorefractive medium. Winiarz et al. reported one such photorefractive medium which consists of hole transporting polymer composite matrix, electro-opticaUy active nanodroplets of liquid crystal and Cadmium sulphide quantum dots as photosentizers (Winiarz and Prasad 2002). They employed poly(methylmethacrylate) (PMMA) as polymer matrix, N-ethylcarbazole (ECZ) as hole transporting medium and commercial nematic liquid crystal mixture TL 202 for fabrication of the photorefractive medium with Cadmium sulphide as photosentizer. The reported medium exhibits more than 90 % internal diffraction efficiency which is relatively high compared with other PDLC photorefractive medium. 

Winiarz JG, Prasad PN (2002) Photorefractive inorganic-organic polymer-dispersed liquid-crystal nanocomposites photosensitized with cadmium sulfide quantum dots. Opt Lett 27 1330-1332... 

Khoo, I. C., Yana Zhang WiUiams, B. Lewis, and T. Mallouk, 2005. Photorefractive CdSe and gold nanowire-doped hquid crystals and polymer-dispersed-liquid-crystal photonic crystals. Mol. Cryst. Liq. Cryst. 446 233-244. 

Khoo, 1. C., Kan Chen, and Y. Wilhams. 2006. Orientational photorefractive effect in undoped and CdSe nano-rods doped nematic liquid crystal Bulk and interface contributions. J. Sel. Top. Quantum Electron 12(3) 443 50 see also Khoo, I. C., Yana Zhang Wilhams, B. Lewis, and T. Mallouk. 2005. Photorefractive CdSe and gold nanowire-doped hquid crystals and polymer-dispersed-liquid-crystal photonic crystals. Mol. Cryst Liq. Cryst. 446 233-244. 

Ono, H., andN. Kawatsuki. 1997. Orientational photorefractive gratings observed in polymer dispersed liquid crystals doped with fullerene. Jpn. J. Appl. Phys. 36 6444 - 6448. 

Steenwinckel DV, Hendrickx E, Persoons A. 2001. Large dynamic ranges in photorefractive NLO polymers and NLO pol5mier dispersed liquid crystals using a bifunctional chro mophore as a charge transporter. Chem Mater 14(4) 1230 1237. 

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