Potentiality of Pr3+- and Pr3+ + Ce3+ -doped crystals for tunable UV upconversion lasers

Gain experiments based on the interconfigurational 4f5d to 4f2 optical transitions in praseodymium-doped fluoride crystals were achieved. The measurements were performed under upconversion pumping of the 4f5d excited configuration via the 3PJ, 1I6 intermediate levels of the 4f2 configuration, using a pump-probe set-up with three synchronized Q-switched nanosecond pulsed lasers. In spite of this two-step excitation, optical losses, due excited state absorption (4f5d→conduction band transition) leading to Pr3+ ion photoionisation and color center formation, were too high to observe any amplification. However, these losses were found definitely weaker in fluoride crystals (Pr:LiYF4, Pr:LiLuF4) than in oxides (Pr:YAlO3) and, probing the 5d→4f emission of Ce3+ under two-step excitation pumping of the Pr3+ 4f5d states in co-doped Pr,Ce:LiLuF4 crystals, no losses were detected at all. © 2002 Elsevier Science B.V. All rights reserved