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Proceedings Paper

Study of relation between crystal structure and laser damage of calcium fluoride
Author(s): Minako Azumi; Eiichiro Nakahata
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Paper Abstract

The artificially grown calcium fluoride is one of key materials for microlithography and used for excimer laser optics etc. Such calcium fluoride is required high laser durability and laser induced bulk damage threshold (LIDT). However, the artificially grown calcium fluoride is not a complete crystal, and there are a lot of sub-grain boundaries inside the crystal that have the possibility of causing degradation of laser durability and LIDT. Moreover, mechanical properties of calcium fluoride are different according to the crystal axis, therefore there is a possibility that mechanical properties influences LIDT. In this study, we examined the relation between crystal structure and LIDT. First, we examined the relation between the crystal axis and LITD of single crystal calcium fruoride. The relation between the crystallographic axis and LIDT that the laser enters was examined. The ArF excimer laser and the fifth high harmonic of the Nd:YAG laser at 213nm were used for the irradiation source of light. We prepared samples that optical axes were <111>, <110> and <001> from the same crystal. From the result of this examination, when the laser irradiated in <111> axis, LIDT was the highest. Next, we observed the damage with polarizing microscope and optical microscope. The result of this observation suggested that the laser damage of calcium fluoride was related to the crystal orientation. Finally, we investigated the damage mechanism of calcium fluoride. It is thought that the laser irradiation induced stress is relaxed most easily when the optical axis is <111>. Therefore, LIDT of calcium fluoride is supposed to be highest when the optical axis is <111>.

Paper Details

Date Published: 3 December 2010
PDF: 7 pages
Proc. SPIE 7842, Laser-Induced Damage in Optical Materials: 2010, 78421U (3 December 2010); doi: 10.1117/12.869770
Show Author Affiliations
Minako Azumi, Nikon Corp. (Japan)
Eiichiro Nakahata, Nikon Corp. (Japan)


Published in SPIE Proceedings Vol. 7842:
Laser-Induced Damage in Optical Materials: 2010
Gregory J. Exarhos; Vitaly E. Gruzdev; Joseph A. Menapace; Detlev Ristau; M. J. Soileau, Editor(s)

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