Spectroscopic analysis of efficient laser material Ho^3+:YVO_4

Abstract

The spectroscopic properties of Ho3+-doped YVO4 were studied at cryogenic temperatures in the 2 µm spectral region to clarify recent observations of efficient dual-wavelength laser operation in this material. Energy levels of the 5I7 and 5I8 manifolds were determined from low-temperature absorption and fluorescence measurements. Polarized absorption cross sections were measured, and stimulated emission cross sections were determined using the reciprocity method coupled with Fuchtbauer-Ladenburg calculations. The observed laser emission wavelengths were at 2054.2 nm and 2068.5 nm. At 80 K, radiative lifetimes for the 5I7 manifold were calculated to be 3.6 ms, and fluorescence lifetimes were measured to be 2.9 ms, indicating a quantum efficiency of ~80%. Analysis of the gain cross section at 80 K and 100 K showed that the laser output wavelength is very susceptible to minor changes in temperature.