Cascade laser oscillation due to Ho3+ ions in a (Cr,Yb,Ho):YSGG yttrium-scandium-gallium garnet crystal

We report obtaining room-temperature laser oscillation in a flashlamp-pumped (Cr,Yb,Ho):YSGG crystal. The laser action, which is due to the Ho³⁺ ions, is based on the cascade of transitions ⁵I₆→⁵I₇→⁵I₈. We have measured the lifetimes of the working levels and the laser wavelength. The efficiency of the energy transfer process Cr³⁺→Yb³⁺→Ho³⁺ is 90%. We investigated the kinetics of the laser action and measured the lasing parameters for various types of output mirrors. We also measured the contribution of the laser transition ⁵I₆→⁵I₇ to the populating of the ⁵I₇ level. For pump energies above 20 J, we observed saturation of the populations of the ⁵I₆ and ⁵I₇ levels of the Ho³⁺ ion. The cause of this saturation is assumed to be a stepwise sensitization of the Ho³⁺ ion. We obtained oscillation in a totally-reflecting resonator at 3-μm without self-limiting.