The formation of color centers induced by irradiation with ArF excimer lasers in CaF2 crystals was found to depend strongly on the sodium impurity concentration. Sodium-related color centers were generated by two-photon absorption because the slope of the induced absorption coefficient just after irradiation started was proportional to the square of the laser fluence. The saturation absorption also depended on laser fluence, and a photobleaching induced absorption phenomenon was observed. We concluded that the saturation absorption level was determined by the equilibrium between two-photon excitation and one-photon reverse reaction.
© 2000 Optical Society of America
(140.2180) Lasers and laser optics : Excimer lasers
(140.3330) Lasers and laser optics : Laser damage
(160.4670) Materials : Optical materials
(220.3740) Optical design and fabrication : Lithography
(300.1030) Spectroscopy : Absorption
Norio Komine, Shigeru Sakuma, Masaki Shiozawa, Tsutomu Mizugaki, and Eiji Sato, "Influence of Sodium Impurities on ArF Excimer-Laser-Induced Absorption in CaF2 Crystals," Appl. Opt. 39, 3925-3930 (2000)