Investigation of the spectral width of quantum cascade laser emission near5.2 mu m by a heterodyne experiment

We report line width measurements of a quantum cascade distributed feedback laser by a heterodyne experiment. At currents slightly above threshold and a laser output power higher than I mW, the full width at half maximum of t he beat signal was narrower than 0.5 MHz, which gives us an upper limit of the laser line width. As reference laser we used a carbon monoxide laser. B oth lasers were operating unstabilized in continuous wave mode emitting lig ht at about 5.2 mum. (C) 2001 Elsevier Science B.V. All rights reserved.