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Reflection Anisotropic Spectroscopy |
RAS measures the difference in reflectance of normal incidence plane-polarized light between two orthogonal directions in the surface plane.
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schematic of the RAS system showing the primary components; xenon light source, calcite polarisers,
quartz photoelastic modulator (PEM), two photodiodes (InGaAs < 1.4 eV, Si above). |
Reflection anisotropy spectroscopy (RAS) measures the difference in reflectance of normal incidence, linearly polarized light between two orthogonal directions in the surface plane [1,2].
The measured anisotropic function of the complex Fresnel reflectivity is given by
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where  x and y are the complex reflection coefficients of light polarized in the x and y directions, respectively. The RAS signal for bulk anisotropic samples is directly related to the complex dielectric tensor components by
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[1]D. E. Aspnes and A. A. Studna, Phys. Rev. Lett. 54(17), 1956–9 (1985).
[2] V. L. Berkovits, I.V. Makarenko, T. A. Minashvili, and V. I. Safarov, Solid State Commun. 56(5), 449–450 (1985).
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