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We describe a method where the standard fabrication of broad area quantum cascade lasers is modified to provide a controlled amount of direct contact of device sidewalls with metal. We demonstrate that this provides sufficient levels of distributed losses to suppress the high order transverse modes in favor of the fundamental or near-fundamental transverse mode operation. We observe that the quantum cascade laser power and slope efficiency are degraded by a small amount, resulting in a large increase in brightness to accompany the power scaling.

Power scaling in broad area quantum cascade lasers results in the operation of high order transverse modes with a far-field profile consisting of two lobes propagating at large angles relative to the optical axis. We report a method of suppressing the high order transverse modes that can extract the fundamental mode and provide emission along the optical axis. By generating a lateral constriction in the waveguide in the form of short trenches defined by the focused ion beam milling technique, we report broad area devices in which most of the power is contained in a near diffraction-limited beam that provides high brightness.

Imaging through deep turbulence is a hard and unsolved problem. There have been recent advances toward sensing and correcting moderate turbulence using digital holography (DH). With DH, we use optical heterodyne detection to sense the amplitude and phase of the light reflected from an object. This phase information allows us to digitally back propagate the measured field to estimate and correct distributed-volume aberrations. Recently, we developed a model-based iterative reconstruction (MBIR) algorithm for sensing and correcting atmospheric turbulence using multi-shot DH data (i.e., multiple holographic measurements). Using simulation, we showed the ability to correct deep-turbulence effects, loosely characterized by Rytov numbers greater than 0.75 and isoplanatic angles near the diffraction limited viewing angle. In this work, we demonstrate the validity of our method using laboratory measurements. Our experiments utilized a combination of multiple calibrated Kolmogorov phase screens along the propagation path to emulate distributed-volume turbulence. This controlled laboratory setup allowed us to demonstrate our algorithm’s performance in deep turbulence conditions using real data.

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