Spectral characterization of a mid-infrared quantum-cascade laser

The spectral characteristics of a mid-infrared quantum-cascade distributed-feedback laser are reported. The laser operated in a continuous-wave single-longitudinal mode at liquid-nitrogen temperature. The output wavelength as a function of input drive current is described over a demonstrated tuning range of 62 GHz. The spectral properties of the laser were observed in a series of measurements taken as the laser's performance gradually degraded. A method is described to perform a linewidth measurement with a precision on the order of 100 kHz using the second harmonic of a CO2 laser. Experimental results demonstrating the feasibility of this technique are reported.