Analysis on the Tm3+, Ho3+ Concentrations in Alumino-Zirco-Fluoride Glass for Efficient 2-µ m Lasing

The dependence of gain coefficients for a Tm3+, Ho3+ co-doped alumino-zirco-fluoride glass on Ho3+ concentration under a 0.79 µ m pumping is described. The calculation of the gain coefficients is made with the upconversion rate constant from the lower coupled ( Tm3+3F4, Ho3+5I7) level to the upper coupled ( Tm3+3H5, Ho3+5I6) level. The gain is determined by measuring absorption coefficients and their appropriate comparison with a simple Tm3+-Ho3+ energy transfer model. The Tm3+, Ho3+ concentrations suitable for eyesafe laser applications at two micrometers are determined as a function of pumping intensity.