A quantum-cascade structure based on a bound-to-continuum design exhibiting a broad gain curve is presented. The full width at half maximum of the measured luminescence spectrum is $\text{297\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ at room temperature. Grating-coupled external cavity lasers using this active region could be tuned over $\text{150\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ (1.45 μm), which is equal to 15% of the free running wavelength $\text{(λ≅10\hspace{0.17em}μ}\mathrm{m}\mathrm{),}$ in pulsed mode at room temperature. Time resolved spectra showed a single-mode operation with a 30 dB side mode suppression ratio after the first 12 ns of the pulse.

A heterogeneous quantum-cascade structure based on two bound-to-continuum designs emitting at 9.6 and $8.4\mu \mathrm{m}$ is presented. Its spontaneous emission spectrum at room temperature has a full width at half maximum of $350{\mathrm{cm}}^{-1}$ and shows a variation of intensity of less than 20% over more than $200{\mathrm{cm}}^{-1}$ . External cavity lasers using a grating in Littrow configuration and antireflection coated chips with this active region could be tuned over $265{\mathrm{cm}}^{-1}$ from $8.2\text{to}10.4\mu \mathrm{m}$ , that is, over 24% of the center wavelength.

A measurement of the linewidth enhancement factor $\alpha$ of a distributed feedback quantum cascade laser is presented. The measurement is based on a heterodyning experiment, in which one of the lasers is modulated at radio frequency. A value of $\alpha =0.02\pm 0.20$ is obtained for a modulation frequency of $500\mathrm{MHz}$ . As the frequency is decreased, $\alpha$ increases and is consistent with a thermal chirp effect.

A strain-balanced, AlInAs/InGaAs/InP quantum cascade laser structure, designed for light emission near 9µm, was grown by molecular beam epitaxy. Laser devices were processed in buried heterostructure geometry. Maximum pulsed and continuous wave room temperature optical power of 4.5 and 2W and wallplug efficiency of 16% and 10%, respectively, were demonstrated for a 3mm by 10µm laser mounted epi-side down on an AlN/SiC composite submount. Pulsed laser characteristics were shown to be self-consistently described by a simple model based on rate equations using measured 70% injection efficiency for the upper laser level.