A strain-balanced, InP-based quantum cascade laser structure designed for light emission at 4.6μm was grown by metal-organic chemical vapor deposition. A maximum total optical power of 1.6W was obtained in continuous-wave mode at 300K for uncoated devices processed in buried heterostructure geometry with stripe dimensions of 5mm by 9.5μm. Corresponding maximum wall plug efficiency and threshold current density were measured to be 8.8% and 1.05kA∕cm2, respectively. Fully hermetically packaged laser of identical dimensions produced in excess of 1.5W under the same conditions.

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A quantum cascade laser structure is demonstrated that provides a broadband gain spectrum of 430 cm−1 with a peak emission wavelength around 4.8 μm. The laser active region is based on multiple transitions from strongly coupled upper states to lower laser states. In spite of the broad gain spectrum, high laser performance was demonstrated with low threshold current density (as low as 1.6 kA/cm2), large slope efficiency (over 5 W/A) and high wall plug efficiency (up to 23%) in pulsed mode operation at 295 K.

Standoff detections of explosives using quantum cascade lasers (QCLs) and the photoacoustic (PA) technique were studied. In our experiment, a mid-infrared QCL with emission wavelength near 7.35 μm was used as a laser source. Direct standoff PA detection of trinitrotoluene (TNT) was achieved using an ultrasensitive microphone. The QCL output light was focused on explosive samples in powder form. PA signals were generated and detected directly by an ultrasensitive low-noise microphone with 1 in. diameter. A detection distance up to 8 in. was obtained using the microphone alone. With increasing detection distance, the measured PA signal not only decayed in amplitude but also presented phase delays, which clearly verified the source location. To further increase the detection distance, a parabolic sound reflector was used for effective sound collection. With the help of the sound reflector, standoff PA detection of TNT with distance of 8 ft was demonstrated.

We investigated the effect of deep-etched mesa sidewall profile and oxide overhang length on the regrowth structural characteristics for buriedheterostructure (BH) quantum cascade lasers (QCLs) grown by metalorganic chemical vapor deposition (MOCVD). The relationship between etched mesa sidewall geometry, oxide overhang length, oxide thickness, and growth uniformity was examined and is extensively discussed. In particular, anomalous growth in the vicinity of the oxide edge resulting from insufficient oxide overhang length was identified and studied. An ideal ratio of mesa height to oxide overhang length between 2.5 and 3.0 is proposed and experimentally justified to yield satisfactory planar regrowths without anomalous growth. Mesas in the ½011 direction with smoothly etched entrant profile yield a higher degree of growth uniformity than mesas in the [011] direction with the re-entrant profile.