An optically-pumped type-Il W laser emitting at 3.4 mu m operated CW u
p to 220 K, with a characteristic temperature of 51 K for the range 78
-220 K. At 78 K, the output power was 90 mW from a 12 mu m wide stripe
, and the differential power conversion efficiency was 2.9% per facet
(uncoated).