Gyrotropy

In concluding we shall consider briefly the calculation of the superlattice linear response with regard to gyrotropy. As before, we assume that the optical properties inside each of the superlattice layers are isotropic. Therefore, for each of the layers with regard to gyrotropy we have (3) ... 

Conversion of electromagnetic wave (EW) polarization provides an efficient and powerful method for diagnostics of media a nd s tructures with reduced symmetry (e.g. anysotropic crystals, media with natural and artificial gyrotropy, periodic structures, solid-state surfaces and thin films). On the other hand, such media and structures can be used as polarization converters. The conversion of the polarization in surface layers and thin films is usually small [1,2] and achromatic because in this case the region of interaction of the EW with the polarization active medium is small and the interaction itself is non-resonant. However, the effect may increase substantially (resonantly) and the polarization converted radiation becomes colored when the external EW excites eigen-oscillations on optically active surface or in an optically active film. For example, under the non-uniform cyclotron resonance excitation in two-dimensional (2D) electron system, high conversion efficiency can be reached [3]. 

The relation (11) should be regarded as an expansion of P(E, N, M) in E, N, and M. We restrict the analysis to the terms that are quadratic in E and linear in N and M. The ratio of the light-wave field E to the magnitude of the intraatomic field E, the ratio = Esu /E of the surface electric field (which breaks the even symmetry at the surface) to E (for N), and the magnitude of the magnetooptical gyrotropy (Af), which is determined by the MO parameter Q and usually satisfies the condition Q 1, are small parameters. Here expansion in N actually means expansion in NE utf, as was shown in reference 35. 

In addition, the ultimate shape of the flake is also mysterious. Thick [ 4 pm] and thin [ 1 pm] AS2S3 flakes tend to become as screws [Tanaka, 2008] and spiral filaments [Fig. 3.13], respectively, for which gyration directions are difficult to experimentally determine. The gyration may be related to photoinduced gyrotropy [Lyubin and Klebanov, 2003], but its mechanism has been left unexplained [DiVincenzo, 1988]. The filamentation may be affected by Kerr self-focusing effects [Polynkin et al., 2011] under photoinduced fluidity. These speculations also remain to be studied. 

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