Characterization of a 10.3-microm pulsed DFB quantum cascade laser

We have measured the output parameters of a 10.3-microm pulsed distributed-feedback (DFB) quantum cascade (QC) laser manufactured by Alpes Lasers and intended for high-sensitivity detection of ammonia and ethylene. The laser beam was collimated with an AR-coated aspheric ZnSe lens with focal length of 11.6mm and clear aperture of 16.5mm. Near- and far-field distributions of the laser emission were recorded with an infrared imaging camera. The fast-and slow-axis laser beam divergences were measured to be 1.2 and 1.4 mrad (FWHM), respectively. The divergence was found to be increasing with injection current. An air-spaced Fabry-Perot interferometer with free spectral range of 0.05 cm(-1) was used to measure the frequency tuning rates of the laser. The laser was tuned by either heat sink temperature, injection current or pulse repetition rate with rates of approximately -8 x 10(-2)cm(-1)K(-1), -7 x 10(-2)cm(-1)A(-1) and -9 x 10(-4)cm(-1)kHz(-1), respectively. The laser frequency decreased linearly with a rate of 10(-2)cm(-1)ns(-1) ( approximately 300 MHzns(-1)) for laser pulses varied from 10 to 50 ns, and the frequency chirp rate was found to decrease for longer laser pulses.