Description of photo-induced light scattering in sbn

9 Characterization of Polar Oxides by Photo-Induced Light Scattering 

This initial optical noise consists of seed waves propagating at angles +9S and -9S with respect to the direction of the pump beam, i.e. in and opposite to the direction of the polar c-axis. Each seed wave ks interferes with the pump wave kp (9.4 (b)) and forms an elementary light interference pattern 

In the case of sbn the phase shift is always exactly = 7t/2 provided that an external electric field is absent (E0 = 0) and there is no frequency shift between the pump and scattered waves. (In the experiments described below, where E0 0, a change of the phase shift 3 of up to 5 % results, which can be neglected. The increase of the space charge field at the maximum field strength of E0 = 4kV/cm is only 15 % in comparison to zero field.) 

The linear electro-optic effect (see Chapter 4) transfers the periodically modulated space-charge field into a refractive index grating  

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