Scientists from Bell Labs in Murray Hill, N.J., have developed an amplifier for quantum cascade lasers that can achieve high-power single-mode emission at a wavelength of 7.4 µm.They used an InGaAs/InAlAs/InP semiconductor amplifier, also based on quantum cascade technology, to attain both high-power emission and improved beam quality from a quantum cascade distributed feedback laser. As described in the June 3 issue of Applied Physics Letters, the amplifier realized peak optical powers of 0.5 W at a temperature of 80 K. In addition, the apparatus showed single-mode operation with a side-mode suppression ratio of 30 dB at temperatures ranging from 10 to 280 K, which allowed the researchers to tune the emission wavelength in the 7.36- to 7.46-µm range.