Photo-induced light scattering

Characterization of Polar Oxides by Photo-Induced Light Scattering... 

This article shows up the possibilities to study ferroelectric media by photo-induced light scattering. In particular the optical characterization of sbn by photo-induced light scattering is reviewed including the determination of optical parameters [7], the investigations of the relaxor-kind phase transition [8] and the analysis of the polar structure [9,10],... 

In this chapter the properties of the relaxor-ferroelectric sbn as well as observation and modelling of photo-induced light scattering in sbn are introduced. 

Figure 9.2 Polarization-isotropic photo-induced light scattering in strontium-barium-niobate doped with 0.66 mol% Cerium (SBN61 Ce). Strongly amplified scattered light occurs in a wide solid angle opposite to the polar c-axis. The label denotes the apex angle measured with respect to the directly transmitted laser beam in air. Ap = 632.8 nm, Ep c. The insets show a photograph of the sbn crystal (left) and the schematic setup of the experiment (right), respectively.

Figure 9.3 Polarization-isotropic photo-induced light scattering in strontium-barium-niobate doped with 0.66mol% Cerium at different times of illumination. Here, the wavelength Ap =...

From this simplified photorefractive model it is straightforward to use the concept of photo-induced light scattering for the optical characterization of polar oxides In sbn, the relation between r33 and the spontaneous polarization P3 = Ps can be written as [15] ... 

These properties demonstrate that the study of photo-induced light scattering can be used to investigate the relaxor-kind phase transition by an optical method. Hereby, various measures can be used, like the temperature dependence of the intensity of the directly transmitted laser beam, of the integrated scattered light and of the intensity ratio R, respectively, as shown in Figure 9.9. 

These results clearly demonstrate that the relaxor-kind phase transition determines the appearance of photo-induced light scattering, and therefore its temperature dependence can be used as a method for optical investigation of phase transitions. E.g., the transition temperature can be determined by the asymmetry parameter as a measure for the symmetry of the scattering pattern or by the comparably simple measurement of the directly transmitted laser beam. 

In this section we show that photo-induced light scattering is a powerful tool, especially to obtain information about the polar structure in the crystal bulk. The polar structure in SBN Ce can be considered as the composition of different periodical and/or quasi-periodical assemblies of ferroelectric 180°-domains distributed in the bulk aligned along the c-axis. The existence of... 

When investigating the polar structure by photo-induced light scattering we assume that the largest contribution to the initial optical noise is due to diffraction of the pump beam on optical inhomogeneities located at boundaries of ferroelectric domains [9], Figure 9.12 illustrates this concept schematically. Internal electric fields Ei (random fields) yield local perturbations 5n of the index of refraction via the linear electro-optic effect 5n = - n rssEi. 

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