Mid-infrared external-cavity quantum-cascade laser

Single-frequency operation of a 10.4-mum room-temperature multimode quantum-cascade laser was achieved by use of a 17-mm short Littrow-type external-cavity configuration. The spectral intensity of the external-cavity laser was increased as much as 20-fold compared with that of a multimode quantum-cascade laser without an external cavity. A single-frequency tuning range of 76 nm (7 cm(-1)) was achieved. The results were obtained without antireflection coating of the laser output facet.