Grating vector

The optical axis defines the j-direction. The x-axis points along the direction of the grating vector, whose absolute value is... 

Figure 8 The phase-shift of PR material of compound 1 as a function of the applied field of steady-state refractive index grating with respect to the writing hght intensity grating. The inset is a typical intensity of the two beams when the grating is moved about 14 im in the direction of the grating vector. The solid line is the theoretical fitting using Eq. (20), with Eq = 99.9 V/p.m. (Reprinted from Ref. 27. Copyright 2000 The American Physical Society.)...

The amplitude of the space charge field is equal to the projection of the applied field in the direction of the grating vector and thus, for moderate fields, is proportional to the poling field poi according to Eq. (8),... 

There is practically no formation of SRG when there is no spatial variation of the optical field, as in the s p and +45 +45 combinations. In addition, there must be a component of the field gradient in the direction of the grating vector, a requirement that is satisfied by the combinations RCPrLCP, p p, and +45 -45. In the eases where there is only spatial variation of the optical field, but no component of the electric field in the grating vectoi the SRG is very weak but a BG, which is a bulk phenomenon, is formed, as in the s s case. These predictions were confirmed experimentally by monitoring the grating formation with orthogonally polarized read beams. 

While the acoustic wave propagates along the grating vector, the diffusive signal (Apdiff) remains where it is created. After the damping of the acoustic wave, the diffusive signal appears. The variation of the temperature is described by the heat diffusion equation and heat generation processes. If the thermal diffusivity [Dlh(m2s 1) = thermal conductivity and... 

From the measured diffraction efficiency 77, it is possible to calculate the refractive index modulation i. Assuming the grating vector is oriented perpendicular to the normal of surface of the sample and that the Bragg condition is met, the following formula [73, 74] is valid ... 

In all the studies discussed, the grating is transmission-type, with the grating vector lying in the sample plane. Using azobenzene-containing polymer-stabilized and polymer-dispersed LCs (PSLCs and PDLCs), Running and coworkers... 

Two standard wave-mixing techniques are commonly used to characterize PR polymers the four-wave mixing and the two-beam coupling technique (43), The samples consist of the polymer sandwiched between two transparent ITO (Indium-Tin-Oxide) electrodes. The external field is applied to the electrodes and is therefore perpendicular to the polymer film. To have a component of the electric field along the grating vector, the sample is tilted as shown in Figure 2. 

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