Quantum-cascade laser produces continuous-wave infrared output

Quantum-cascade laser produces continuous-wave infrared output

Federico Capasso and coworkers at AT&T Bell Laboratories (Murray Hill, NJ) demonstrated operation of gallium indium arsenide/aluminum indium arsenide (GaInAs/AlInAs) quantum- cascade lasers at several infrared wavelengths. They obtained 1 mW of single-mode CW output at 8.3 µm and 80 K, as well as multimode 7.8-µm CW powers as high as 6 mW at 77 K. Single-mode output at 7.8 µm is around 1-2 mW. Capasso reports the output powers and effective operating temperatures are significantly higher for pulsed operation. At 200 K, 6 mW at 8 µm was recorded, while an even higher power of 20 mW was measured from a 4.3-µm device.

Unlike conventional semiconductor lasers, in which the bandga¥defines the emission wavelength, the emission wavelength in quantum-cascade lasers is determined by the thickness of the quantum-well layers, and these devices are predicted to extend from 3.5 µm to about 10 µm. The grou¥is trying to develo¥these as an alternative to lead-salt diode lasers, citing beam quality and single-mode CW operation as advantages of the technology. Currently, liquid nitrogen cooling is required for lasing, but the goal is to bring operating temperature u¥to 200 K so thermoelectric cooling can be used.