<title>F<formula><inf><roman>2</roman></inf></formula>-laser-induced damage on transparent fluoride crystals</title>

Abstract

For the application of F2 lasers to micro-I 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 CaP2 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 LiCaA1F6 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 LiCaAIF6 was similar to that of VUV grade CaF2 while that ofBaF2 was about halfofthe other two fluoride crystals.