Photorefractive gratings formation

Charge transport is one of the important processes that control the speed of the PR index grating formation and the PR sensitivity. According to the standard theory of photorefraction [21], the response time for the formation and erasure of the space-charge field [xr in Eq. (21)] is proportional to the dielectric relaxation... 

The chromophores serve for the formation of efficient photorefractive gratings and they are photo-chemically active, probably by 2 -n 2 photochemical reactions, when triplet sensitized. The photorefractive external diffraction efficiency is highly dependent on the glass transition temperature of the composites. A low glass transition temperature favors the efficiency. 

Not surprisingly, different material functions are required for each of the steps in the formation of a photorefractive grating, leading to development of multifunctional composite materials and the search for optimal combinations of material properties as discnssed in Composition of Polymeric Photorefractive Materials section. 

Photoconductivity. As outlined in Introduction section, the first three steps of the photorefractive process are related to photoconduction, which controls the rate of grating formation and the amplitude of the charge grating, as well as the rate of erasure imder imiform illumination. Therefore, to imderstand and optimize the physical processes involved in photorefractive pol5miers, it is... 

Figure 8.11 Mechanism of formation of photorefractive grating (a) iiiumination pattern creating charge carriers (b) charge redistribution and direction of internai space charge field and (c) final refractive index grating.

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