Grating-coupled external-cavity quantum-cascade lasers were studied for tem
peratures from 80 to 230 K. At 80 K, a tuning range of similar to 65-88 nm
are obtained for 4.5 and 5.1 mum laser amplifiers, respectively. The tuning
ranges for both narrowed substantially with increasing temperature, to sim
ilar to 23 nm at 203 K. The threshold varied slowly versus wavelength, whil
e the efficiency appeared to be close to optimum toward wavelengths shorter
than the free running wavelength. (C) 2001 American Institute of Physics.