Pyroelectric mechanism of the holographic grating recording

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Abstract
Spatial variation of the refractive index of a pyioelectric crystal due to illumination by nonhomogeneous light is theoretically considered. The action of light leads to an electric field due to the pyroeffect and can also create photoelectrons which diffuse and drift in this field. It is the electrooptical effect that is responsible for the variation of refractive index. The stationary solution is obtained. The derivation of the solution consists of determining the temperature distribution caused by nonhomogeneous illumination from the heat conduction equation, and the electrical field distribution from the Maxwell equations and from the material equation of the pyroelectric substance, the temperature dependence of the spontaneous polarization value being taken into account. In particular, the Landau model is investigated (a ferroelectric plate with periodically alternated transverse domains of equal size), and a monodomain plate with polar axes lying in its plane. The possibility of an effective holographic record using the pyroelectric effect in ferroelectrics is shown to result from the calculation. Strong dependence of the variation of the refractive index δn on the size of the light stripe Λ is a characteristic feature of the mechanism. Value of δn calculated as an example for potassium dihydrogenphosphate with λ ∼ 1 μm and with strong absorption (kl 1, where k is the absorption coefficient -100 cm-1, J. is width of the plate), amounts to ∼10-4 in the centre of the light stripe, the power of the illumination being 0.1 W/cm2.