Tunable diode lasers (TDL) that emit in the middle infrared (MIR) wavelength range are widely used sources of coherent light in absorption spectroscopy techniques, such as high-resolution molecular spectroscopy and atmospheric trace gas analysis. One of the most important designations of these technologies is the detection of air pollutants such as carbon monoxide, carbon and sulfur dioxides, nitrogen oxides, ammonia and methane, and other toxic and undesired environmental species. Owing to their narrow linewidth and high spectral brightness, the use of MIR TDL provides for a very low detection limit in the “parts per billion” range. Other attractive features include simple and fast tuning of the wavelength, robustness, and relatively low cost.

A. Andrejew and his co-authors in this Optics Letters article have designed GaSb-based Vertical-Cavity Surface-Emitting Lasers (VCSELs) with emission wavelength at 3 μm. From the application point of view, this achievement has two promising highlights. First, this wavelength range is of particular interest, since many technologically important gases have strong absorption lines between 2 and 3 μm. Second, designed VCSELs are inherently longitudinally single-mode lasers with an output beam of Gaussian profile, allowing to use simple and inexpensive optics. From the technological point of view, a concept with the undoped epitaxial AlAsSb/GaSb bottom DBR is a promising for mid IR wavelength VCSELs, since avoiding the doped epitaxial mirror considerably reduces unwanted optical losses.

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