Abstract We report on the continuous-wave and passively Q-switched operation of a compositionally “mixed” heavily doped 16.6 at.% Yb:(Y,Lu) 3 Al 5 O 12 garnet crystal at cryogenic temperatures (100–200 K), pumped by volume Bragg grating stabilized diode laser emitting 969 nm. At 140 K, in regime, maximum output power 10.65 W was achieved ~ 1029 nm with slope efficiency 56% (versus incident pump...