Temperature Changes Induced by Sinusoidal Optical Intensity

DENSITY AND TEMPERATURE CHANGES INDUCED BY SINUSOIDAL OPTICAL INTENSITY 

As an example of how one may gain some insight into such a complicated problem, and for other practically useful reasons, we now consider the case where the optical intensity is a spatially periodic function (i.e., an intensity grating). Such an intensity function may be derived from the coherent superposition of two laser fields on the liquid crystal (see Fig. 9.4). 

The diffractions from the probe beam in the 0 directions are termed first-order diffractions. The efficiency of the diffraction r, defined by the ratio of the intensity of the diffraction to the zero-order (incident) laser intensity, is given by  

The optical intensity inside the liquid crystal is of the form Ep-=Ei +E2+2 ExE2 cos ((ki - k2) r) in the plane wave approximatioa The dc part of E gives rise to spatially uniform changes in p and T, and they do not contribute to the dilfiaction of the beam. We may therefore consider only the spatially periodic part and write i =2 i 2 cos(q y), where q=k]-k2. Furthermore, for simplicity as well as convenience, let E = 2 =-E o- This gives 

For 0 t Xp, where is the dmation of the laser prrlse (assumed to be a square pulse). 

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