Abstract

Upconversion emission at 480 nm in Tm:LaF₃ crystals was reported with continuous excitation in the red[l] and the excitation at 635.2 nm produced photon avalanche upconversion emission. However, the upconversion emission has not been investigated in this crystal for pulse laser excitation. In this paper, we report the separation of two kinds of two-step upconversion processes for the blue upconversion emission in the crystal. One process is a single pulse sequential two-step absorption process of the ³H₆ → ³F₂ and ³H₄ → ¹D₂ transitions and the other two-step absorption process is produced by the successive pulse excitations from ³H₆ to ³F₂ and from ³F₄ to ¹G₄. Pulse repetition rate dependence of the emission at 480 nm with an excimer-laser pumped dye laser excitation in Fig.1 shows the separation of two upconversion processes. The emission at 656 nm excitation even with 1 Hz indicates the single pulse two-step upconversion, although it increases due to the accumulation of the population in the ³H₄ level when the repetition rate does.

© 1998 IEEE