Photon avalanche upconversion in Er/sup 3+/:YAlO/sub 3/

The results of an investigation of photon avalanche upconversion pumping in Er/sup 3+/:TiAlO/sub 3/ are reported. Five pump wavelengths corresponding to transitions from the metastable /sup 4/I/sub 13/2/ state to the /sup 2/H/sub 11/2/ state generated upconversion laser emission at 549.8 nm. The dependence of the laser output power on pump power near laser threshold is discussed in terms of a four-level kinetics model and is shown to reflect the threshold power requirement for photon avalanche. The maximum output power at 7 K was 33 mW, giving an optical conversion efficiency of 3.5% and a conversion efficiency of 28% based on absorbed power. Pumping Er:YALO by cross relaxation energy transfer produced 166 mW of laser output with an optical conversion efficiency of 17%.<
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