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Journal of Micro/Nanolithography, MEMS, and MOEMS

Short wavelength optical anisotropy in CaF2 caused by exciton dispersion
Author(s): Martin Letz; W. Mannstadt; Matthias Brinkmann; Lutz Parthier; G. Wehrhan; Ewald Moersen
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Paper Abstract

Based on exact symmetry considerations one can show that a cubic system is always optically isotropic. Nevertheless even a perfectly cubic crystal such as CaF2 can show small optical anisotropy when interacting with light. Resolving this seeming contradiction leads to a phenomenon called spatial dispersion, which is an enhancement of optical anisotropy. While the initial tiny anisotropy is caused by the symmetry breaking of light, the enhancement that makes the effect observable is provided by the vicinity of a strong absorption. In semiconductors such an absorption is mainly given by the band gap but in an ionic crystal such as CaF2 the bound electron-hole pair, a deep excitonic two-particle bound state, is an additional strong absorption causing response functions to diverge as ω-ω0–1 in its vicinity, where ω0 is the bound state energy. We show that the exciton dispersion is able to explain in all details the optical anisotropy observed in CaF2 including the spatial-dispersion-induced birefringence, the so-called "intrinsic birefringence." As opposed to normal birefringence, the effect in CaF2 does not show up at large wavelengths and has seven optical axes instead of one.

Paper Details

Date Published: 1 April 2003
PDF: 7 pages
J. Micro/Nanolith. MEMS MOEMS 2(2) doi: 10.1117/1.1563262
Published in: Journal of Micro/Nanolithography, MEMS, and MOEMS Volume 2, Issue 2
Show Author Affiliations
Martin Letz, Schott Glas (Germany)
W. Mannstadt, Schott Glass (Germany)
Matthias Brinkmann, Schott Glas (Germany)
Lutz Parthier, Schott Lithotec AG (Germany)
G. Wehrhan, Schott Lithotec AG (Germany)
Ewald Moersen, Schott Lithotec AG (Germany)

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