Abstract

Ho³⁺ can be sensitized by Cr³⁺ and Tm³⁺ in YAG. The efficient pump mechanism consists of a double-step energy transfer process Gr:Tm and Tm:Ho. At high concentrations (~8 × 10²⁰ cm⁻³) the Tm³⁺ ion acts as an efficient acceptor of the energy absorbed by the Cr³⁺ ions. A Tm:Tm cross-relaxation converts the excitation energy down to the IR region with a quantum efficiency of ~1.8. To operate the 2-μm Ho laser, the Ho concentration must be low to avoid too large reabsorption losses. Nevertheless, even at low Ho concentrations the Tm:Tm energy migration leads to an efficient Tm:Ho energy transfer. These effects could be directly observed under laser pumping of Cr:Tm:Ho:YAG, where we achieved power slope efficiencies of more than 40% when pumping at a 647.1-nm wavelength.

© 1988 Optical Society of America