For the application of F₂ lasers to micro-/nano-fabrication including photolithography, one of the important research subjects is to eliminate the chromatic aberration, and combination of lenses made of two optical materials with different refractive indices is the effective way. However, only CaF₂ is widely applied to lenses for a vacuum ultraviolet (VUV) beam, and a "second material" to be paired with CaF₂ is strongly requested. Here, we examined two fluoride crystals which are transparent in the VUV region, BaF₂ and LiCaAlF₆ grown by the Czochralski technique, as candidates for VUV optics. We investigated the change of the VUV transmittance and the onset of optical damage of these fluoride crystals against F₂ laser irradiation. These crystals showed good optical tolerance against cumulative F₂ laser irradiation, and the damage threshold of LiCaAlF₆ was similar to that of VUV grade CaF₂ while that of BaF2 was about half of the other two fluoride crystals.

Date Published: 8 October 2004
PDF: 6 pages
Proc. SPIE 5662, Fifth International Symposium on Laser Precision Microfabrication, (8 October 2004); doi: 10.1117/12.596411

Published in SPIE Proceedings Vol. 5662:
Fifth International Symposium on Laser Precision Microfabrication
Isamu Miyamoto; Henry Helvajian; Kazuyoshi Itoh; Kojiro F. Kobayashi; Andreas Ostendorf; Koji Sugioka, Editor(s)