We present the development of a broad gain quantum cascade active region. By appropriate cascade design and using a symmetric active region arrangement, we engineer a flat gain and increase the total modal gain in the desired spectral range. Grating-coupled external cavity quantum cascade lasers using this symmetric active region are tunable from 7.6 to 11.4 μm with a peak optical output power of 1 W and an average output power of 15 mW at room-temperature. With a tuning of over 432 cm−1, this single source covers an emission range of over 39% around the center frequency.

We present a model to a priori calculate the temperature and field dependent intersubband linewidth of the optical transition in quantum cascade laser designs. Besides intra- and intersubband lifetime broadening, it comprises interface roughness scattering based on the approach of Tsujino et al. [Appl. Phys. Lett. 86, 062113 (2005)]. We verified our model with experimental data of quantum cascade lasers having different linewidths. Excellent agreement with the experiment was found for the two-phonon resonance design. Linewidths are slightly overestimated in the bound-to-continuum design. Differential gain and threshold current density are in excellent agreement for the two-phonon resonance design. Although the slope efficiency is somewhat underestimated at low temperatures, there is still reasonable agreement with the experiment.

GaAs-based quantum-cascade lasers based on a bound-to-continuum transition have been realized and characterized. This band structure design combines the advantages of the well known three-well and superlattice active regions. We observed lasing of Fabry–Pérot lasers in pulsed mode up to a temperature of 100 °C. Multimode emission with a pulsed peak power of 340 mW is observed at room temperature and 42 mW at 80 °C. Further, from aging tests we expect a lifetime of over 60 years for these devices.

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The design, construction and characterization of a novel circular multipass cell for sensitive trace gas analysis are presented. This cell allows for easy modification of the optical path length without any changes of its physical parameters. Furthermore, it is suited for three different detection techniques: direct absorption, wavelength modulation and photoacoustics. To demonstrate its performance, mixing ratios of 13 CO 2 and N 2 O were measured from ambient air, using a quantum cascade laser. With the direct absorption method, noise equivalent 1-s precisions of 2.7 ppb and 0.2 ppb are achieved for 13 CO 2 and N 2 O, respectively. The wavelength modulation technique resulted in 4.3 ppb precision with 1-s averaging for the 13 CO 2 measurements. A Q-factor of 190 and a normalized noise equivalent minimum absorption of 1.3 × 10 −8 cm −1 W Hz −1/2 are achieved using the photoacoustic technique.A. Manninen ( ) · B. Tuzson · L. Emmenegger

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