IMAGING OPTICS

Short wavelength optical anisotropy in CaF2 caused by exciton dispersion

[+] Author Affiliations
M. Letz, W. Mannstadt, M. Brinkmann

Schott Glas, Research and Development, 55014?Mainz, Germany

L. Parthier, G. Wehrhan, E. Mo¨rsen

Schott Lithotec AG, Otto-Schott Strass. 13, 07745?Jena, Germany

J. Micro/Nanolith. MEMS MOEMS. 2(2), 112-118 (Apr 01, 2003). doi:10.1117/1.1563262
History: Received Jul. 5, 2002; Revised Nov. 22, 2002; Accepted Dec. 16, 2002; Online April 11, 2003
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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 (ωω0)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.© 2003 Society of Photo-Optical Instrumentation Engineers.

© 2003 Society of Photo-Optical Instrumentation Engineers

Citation

M. Letz ; W. Mannstadt ; M. Brinkmann ; L. Parthier ; G. Wehrhan, et al.
"Short wavelength optical anisotropy in CaF2 caused by exciton dispersion", J. Micro/Nanolith. MEMS MOEMS. 2(2), 112-118 (Apr 01, 2003). ; http://dx.doi.org/10.1117/1.1563262


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