Orientational photorefractivity

p is a material parameter, V is the applied voltage, and d is the sample thickness. 

DMNPAA and DHADC-MPN (see Chart 4.2) are typical optically anisotropic compounds with permanent dipole moments, which can be oriented in an electric field at room temperature in formulations plasticized with ECZ and, therefore, have low Tg values. Typical values reported in the literature are p=86 cm V for the system DMNPAA PVK ECZ TNF and p=333 cm for the system DHADC-MPN PVK ECZ TNFDM [10]. 

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In this section, we will first provide a short discussion on some of the basics of the design of photorefractive polymers. Then we will review some of the basic physical properties such as photogeneration and transport in organic amorphous materials needed to develop and understand photorefractive polymers. We will describe the orientational photorefractive effect that is used in most of today s low glass transition temperature materials. Finally we will describe selected examples of photorefractive polymers and describe their optical and electrical properties. 

Figure 8.13. (a) Schematic depiction of the optical wave mixing configivalion to stu orientation photorefractivity of nematic liquid crystal under ac bias, (b) Schematic showing various space charge fields involved in the orientational photorefractive effect in nematic liquid crystals. 

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. 

Khoo, I. C. 1996. Orientational photorefractive effects in nematic liquid crystal films. IEEE J. Quantum Electron. 32 525-534. 

Khoo, I. C., H. Li, and Y. Liang. 1974. Observation of orientational photorefractive effects in nematic Uquid crystals. Opt. Lett. 19 1723. 

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

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