Characterization of a 10.3-μm pulsed DFB quantum cascade laser

We have measured the output parameters of a 10.3-μm 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 11.6 mm and clear aperture of 16.5 mm. 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 ∼−8 × 10−2 cm−1 K−1, −7 × 10−2 cm−1 A−1 and −9 × 10−4 cm−1 kHz−1, respectively. The laser frequency decreased linearly with a rate of 10−2 cm−1 ns−1 (∼300 MHz ns−1) for laser pulses varied from 10 to 50 ns, and the frequency chirp rate was found to decrease for longer laser pulses.