We have observed persistent spectral hole burning (PSHB) in Eu<sup>3+</sup> -doped sodium borate glasses irradiated with near-IR femtosecond laser pulses. As-prepared glasses, i.e., glasses melted in air, do not show PSHB even at low temperatures (~77K) , but room-temperature PSHB occurs in the irradiated glasses. The exposure to IR radiation causes both the reduction of Eu<sup>3+</sup> to Eu<sup>2+</sup> and the formation of intrinsic defects. We propose that the photoinduced redistribution of electric charges between Eu<sup>3+</sup> to Eu<sup>2+</sup> is responsible for the occurrence of PSHB.
© 2001 Optical Society of America
Koji Fujita, Masayuki Nishi, and Kazuyuki Hirao, "Ultrashort-laser-pulse-induced persistent spectral hole burning of Eu3+ in sodium borate glasses," Opt. Lett. 26, 1681-1683 (2001)