Abstract
Infrared laser pumping of Tm:LiYF4 at low temperatures on a transition between excited states leads to strong visible and ultraviolet fluorescence. These effects are believed to arise from a multistep process. In the first step photon avalanche excitation creates a population of Tm3+ ions in states near 15 000 cm−1 and below. This step is followed by several energy transfer steps that populate levels up to 35 000 cm−1. Upconversion is shown to be much stronger under avalanche (excited-state) pumping than under conventional pumping from the ground state into the same upper state.
© 1993 Optical Society of America
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