<title>Solarization of AlF<formula><inf><roman>3</roman></inf></formula>-based fluoride glasses for VUV optics by ArF excimer laser irradiation</title>

Abstract

Color center formation in AlF<SUB>3</SUB>-YF<SUB>3</SUB>-RF<SUB>2</SUB> (R equals alkaline earth metal) glasses doped with PO<SUB>2.5</SUB> (0 - 3 mol %) by irradiation with ArF excimer laser light was examined by optical absorption (vuv-visible) and electron paramagnetic resonance spectroscopies. Impurity iron ions and oxygens in the samples were 0.2 ppm and 440 ppm, respectively. Optical absorption ranging from 2 - 8 eV was induced via one-photon absorption processes. The optical band dominating the transmission loss at 193 nm has the peak at 5 eV in the P-free glasses or the peak at 6.9 eV in the doped glasses. The origins of the 5 ev-band and the 6.9-ev were tentatively ascribed to an oxygen-related hole center giving an EPR signal at g equals 2.0097 and PE'-center giving a hyperfine doublet with a separation of approximately 70 mT. The oscillator strengths of the 5-ev band and the 6.9-ev band were calculated as approximately 0.2 and approximately 0.13, the latter being close to that of Si E'-center. No formation of color centers associated with Al, Y, R and F ions was observed. The present results suggest that the reduction of impurity oxygen is a route to effectively suppress the solarization in the P-free AlF<SUB>3</SUB>-based glasses.