We report on room-temperature, continuous-wave operation of single-mode quantum cascade lasers designed for
minimal threshold power consumption in the 4 to 10 μm spectral range. Narrow-ridge distributed feedback lasers were
developed with plasma-etched sidewall corrugations and infrared-transparent dielectric cladding, enabling fabrication
without any epitaxial steps beyond the initial growth of the planar laser wafer. The devices exhibit single-mode emission
with stable, mode-hop-free tuning and side-mode suppression greater than 25 dB. We demonstrate packaged single-mode
devices with continuous-wave threshold power consumption near 1 W above room temperature.
We report a surface-emitting THz source based on intracavity difference-frequency generation in dual-wavelength midinfrared
quantum cascade lasers with integrated giant second-order nonlinear susceptibility. The THz light is coupled out
of the waveguide by a second-order grating etched into the laser ridges. In contrast to sources where the difference-frequency
radiation is emitted from the facet, this approach enables extraction of the THz emission from the whole
length of the device even when the coherence length is small. We also studied the properties of the mid-infrared pump
beams and found that due to gain competition, mid-infrared modes tend to start lasing in higher order lateral modes. The
mid-infrared mode with the lower threshold current reduces population inversion for the second laser with the higher
threshold current due to stimulated emission. We developed a rate equation model to quantitatively describe mode
interactions due to mutual gain depletion.
Wavelength beam combining was used to co-propagate beams from 28 elements in a linear array of distributedfeedback
quantum cascade lasers (DFB-QCLs). The overlap of the beams in the far-field is improved using
wavelength beam combining; the beam-quality product of the array, defined as the product of near-field spot
size and far-field divergence for the entire array, was improved by a factor of 21. We measured the absorption
spectrum of isopropanol at a distance of 6 m from the laser arrays, demonstrating the efficacy of wavelength
beam combined DFB-QCL arrays for remote sensing.
We report second-harmonic and sum-frequency generation in GaAs based quantum cascade lasers. Different waveguide designs and active regions were investigated as well as a doping dependence study of the second-order susceptibility in one of the investigated structures is shown. We present farfield measurements which give information about the modal behavior depending on the waveguide design and dimensions. We also demonstrate that grating-coupled surface emission is a highly efficient way to couple out the second-harmonic radiation.
In this paper we present single mode quantum cascade lasers (QCLs) based on the GaAs and the InP material systems. We show results for first- and second-order distributed feedback (DFB) QC lasers with surface gratings. The InP based lasers are grown by metalorganic vapor phase epitaxy (MOVPE) and show single mode continuous wave emission up to 200 K. In pulsed operation we achieved single mode surface emission peak output powers exceeding 1 Watt at room temperature. The presented GaAs/AlGaAs laser features an air/AlGaAs waveguide, combined with a second-order distributed feedback grating. That laser shows 3 Watts of single mode output power via the surface at 78 K.
We report MOVPE-grown quantum cascade lasers with operating wavelengths between λ~7.5-9.5μm with threshold current densities as low as 2.4kA/cm2 at room temperature. Seven wafers grown for operation at ~9μm show a variation of just 3% in the superlattice periods obtained from X-ray analysis, and laser emission is observed from all wafers with a ~5meV spread of emission energies. Multimode Fabry-Perot and singlemode distributed feedback lasers have been fabricated, operating at λ~7.8μm at room temperature, corresponding with absorption lines in the infrared spectra of methane. In addition, we have produced a strain compensated MOVPE-grown quantum cascade laser operating at λ~4.5μm.