Abstract
We present a comprehensive spectroscopic study of the possible room-temperature green laser transition in Because of the low phonon energies, 270 cm-1 in the otherwise multiphonon-quenched and levels are metastable and can serve as intermediate pump and upper laser levels, respectively, for a green upconversion laser excited at 800 nm. Polarized spectra of ground-state and excited-state absorption at 800 nm and of emission at 560 nm are measured, and the corresponding absorption and emission cross sections are derived. Luminescence-decay measurements provide lifetime data. Despite the large number of metastable levels of in a low-phonon host material, luminescence spectra and intensity-versus-power measurements reveal that the energy dissipation into levels other than those required for the operation of the laser transition (i.e., is small at low dopant concentrations. At higher concentrations, an energy-transfer upconversion process populates the lower laser level and counteracts inversion. The theoretical pump threshold of the proposed upconversion-laser transition under cw and pulsed excitation is derived.
© 2000 Optical Society of America
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