Birefractive Effects in Crystals and Quantum Wells
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ZALAMAI, Victor, SYRBU, Nicolae. Birefractive Effects in Crystals and Quantum Wells. In: Multidisciplinarity in Modern Science for the Benefit of Society, 21-22 septembrie 2017, Chișinău. Chișinău, Republica Moldova: Inst. de Fizică Aplicată, 2017, p. 38. ISBN 978-9975-9787-1-2.
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Multidisciplinarity in Modern Science for the Benefit of Society 2017
Masa rotundă "Multidisciplinarity in Modern Science for the Benefit of Society"
Chișinău, Moldova, 21-22 septembrie 2017

Birefractive Effects in Crystals and Quantum Wells


Pag. 38-38

Zalamai Victor1, Syrbu Nicolae2
 
1 Institute of Applied Physics, Academy of Sciences of Moldova,
2 Technical University of Moldova
 
Disponibil în IBN: 16 martie 2018



Teza

Double refraction or birefringence is an effect of the light splitting into two components in anisotropic media. If a light ray falls perpendicular to the surface of the crystal, then on this surface it splits into two rays. The first ray continues to propagate directly, and is called ordinary; the second ray is diverted to the side, and is called extraordinary. It was first discovered by the Danish scientist Rasmus Bartholin on a crystal of Iceland spar (calcite) in 1669. When light waves propagate along the c axis in ZnP2 crystals of D4 8 symmetry, optical activity (rotation of the polarization plane of light waves) is observed. In directions perpendicular to the optical axis c, it is absent. In these directions, the crystal has a linear birefringence. The refractive indices for the polarizations E||a and E||b intersect at a wavelength of 612 nm (λ0). This point is named isotropic point or isotropic wavelength. At a temperature of 9 K, the wavelength λ0 is shifted to the short-wave region in accordance with the temperature coefficient of the displacement of the absorption edges for the polarizations E_c and E||c. Such a crystal is a phase plate in which two light waves propagate with different velocities. CdGa2S4 crystals possess a natural optical activity. The symmetry of the crystal CdGa2S4 (the space group S4) is such that the optical activity along the c axis is absent and manifests itself only in directions perpendicular to this axis, where it is weak in comparison with linear birefringence. For this reason, it is possible to observe the gyrotropy in its pure form. The anisotropy of the optical spectra at 300 and 10 K of ZnAl2Se4 crystals doped with cobalt is investigated. The intersection of the spectral dependences of the refractive index for ordinary and extraordinary light waves (isotropic wavelengths - λ0, λ01, λ02 and λ03) is found in the region of electronic transitions from the levels of Co2+ ions and in the depth of the absorption band (λ04, λ05, λ06 and λ07). It is established that the spectral dependence Δn = n(E_c) - n(E||c) intersects the zero axis for all values of isotropic wavelengths, both in the transparency region and in the depth of the absorption band. The bands of the reflection spectra of crystals in parallel and crossed polarizers at isotropic wavelengths have a half-width of ~ 7-15Å. The absorption coefficient at isotropic wavelengths varies from 10 to 103 times. On ZnAl2Se4 crystals doped with cobalt, narrow-band filters for various wavelengths can be created. Reflective spectra had been researched in In0.3Ga0.7As quantum layers, modulated by the reflection and transmittance wavelength at P, P (S, S) and 450, 450 (1350, 1350) light-wave polarizations at an incident angle near to the normal and Brewster ones. Isotropic wavelengths λ0 1.137 μm (1.09 eV), λ02 - 1.11 μm (1.12 eV) and λ03 – 0.932 μm (1.09 eV) had been revealed. The refractive indexes n for P, P (S, S) and 450, 450 (1350, 1350) are intersecting for these wavelengths and theirs difference Δn = nPP - nSS (Δn = n(450) - n(1350)) intersects the null axis. The isotropic wavelength (λ0) is shifted towards the long wavelength region at Brewster angle in reference to the case of perpendicular incidence of light (ц = 70) on the QW surface.