In this article we present our latest work on the optimization of mid-infrared quantum cascade laser fabrication techniques. Our efforts are focused on low dissipation devices, broad-area high-power photonic crystal lasers, as well as multi-wavelength devices realized either as arrays or multi-section distributed feedback (DFB) devices. We summarize our latest achievements and update them with our most recent results.

We report on the dynamic behavior of dual-wavelength distributed feedback (DFB) quantum cascade lasers (QCLs) in continuous wave and intermittent continuous wave operation. We investigate inherent etaloning effects based on spectrally resolved light-current-voltage (LIV) characterization and perform time-resolved spectral analysis of thermal chirping during long (>5 µs) current pulses. The theoretical aspects of the observed behavior are discussed using a combination of finite element method simulations and transfer matrix method calculations of dual-section DFB structures. Based on these results, we demonstrate how the internal etaloning can be minimized using anti-reflective (AR) coatings. Finally, the potential and benefits of these devices for high precision trace gas analysis are demonstrated using a laser absorption spectroscopic setup. Thereby, the atmospherically highly relevant compounds CO₂ (including its major isotopologues), CO and N₂O are simultaneously determined with a precision of 0.16 ppm, 0.22 ppb and 0.26 ppb, respectively, using a 1-s integration time and an optical path-length of 36 m. This creates exciting new opportunities in the development of compact, multi-species trace gas analyzers.

Synthetic Aperture Radar (SAR) is the only remote sensing technology that can provide high resolution images in adverse weather conditions and in day or night times. It is thus is a powerful tool for Earth monitoring. Certain applications, such as disaster relief, military reconnaissance and ice-flow and ship monitoring require a continuous flow of high-resolution images covering large areas; however, given the large amount of complex data generated and system limitations of data bandwidth and processing speed, not all the requirements can be met at the same time. In addition, multiple user requests are often submitted to the SAR system platform, and not all can be addressed, again due to limitations of area coverage. Increasing the speed of SAR processors and processing on-board are two ways to improve the SAR data throughput and therefore to meet the operational needs of all users. This paper discusses an optronic SAR processor capable of rapidly processing full-scene multi-looked images. Details of the processor design and image results are discussed. Estimations for speed and image throughput are provided, all presented in the context of the requirements for operational service of the various applications.

A laser exhibits both controllable gain and loss and, under proper design conditions, is an ideal non-Hermitian system allowing the direct observation and engineering of spectral singularities such as exceptional points (EPs). A dual section distributed feedback (DFB) quantum cascade laser (QCL) is a prototype of such a system, allowing the controlled coupling of a ladder of cavity Fabry–Perot modes to a quarter wave shifted DFB mode. Tuning the coupling strength and the gain difference between these two set of modes enables probing the regimes from weak coupling to strong coupling and the robust observation of EP singularities. At these EPs, the laser exhibits a sequence of lasing and switching off the coherent emission when pumped above transparency. Additionally, the pumping scheme allows the deliberate lifting of the EP degeneracy. These results show that dual section QCL is a perfect platform to study EPs because the coupling parameter and system loss can be tuned in a single device.

Quantum cascade lasers (QCLs) are powerful semiconductor light sources, based on intersubband transitions, which can be tailored to operate in the mid-infrared (MIR) region of the electromagnetic spectrum [1]. This region is of particular interest for applying various gas absorption spectroscopy schemes, as many of the characteristic transitions of several gas molecules occur at energies that are situated in this region [2].