Spectroscopic and laser investigations of Mn5+:Sr5(VO4)3F
Résumé
Mn:Sr5(VO4)3F has been investigated as a laser material for operation near 1200 nm. Absorption and emission spectra are consistent with Mn5+ substitution into the distorted tetrahedral V5+ sites of this apatite crystal. Emission is almost entirely from the 1E state, resulting in a room-temperature fluorescence lifetime of 475 μs. Together with a peak stimulated emission cross section of about 1×10−19 cm2 and strong, broad absorption bands, this is attractive for lamp- or diode-pumped laser operation. However, the 1E emission makes Mn:Sr5(VO4)3F a three-level system. Laser operation has been demonstrated at room temperature, but the efficiency is lower than expected. Single-pass gain measurements and saturable absorption and fluorescence data indicate that the primary difficulty is excited-state absorption at the pump wavelength. This absorption is very broad, and is probably due to 1T1 and 1T2 excited states.