Efficient InSb laser with resonant longitudinal optical pumping

External quantum efficiency of greater than 20 percent was achieved from tunable cw InSb lasers resonantly pumped with a CO laser. Thin InSb platelets at less than 10 K were pumped in a longitudinal geometry with the InSb recombination emission parallel to the CO radiation. Single-longitudinal-mode operation with power up to 10 mW was achieved with a 0.1 to 0.3-cm-1 linewidth, mechanically or thermally tunable over several cm-1. Magnetic-field effects on the threshold and emission frequency were also studied