28 August 2020 Fundamental mode emission in tapered quantum cascade lasers for high brightness
Mykhaylo P. Semtsiv, William T. Masselink
Author Affiliations +
Abstract

Currently, the highest power quantum cascade lasers (QCLs) include (i) an efficient active region design, which minimizes the energy fraction transferred into heat, (ii) a relatively large number (40) of cascades, which increases the mode confinement factor, Γ, and (iii) narrow buried-heterostructure waveguides, which efficiently cool the active region through efficient lateral heat flow. This combination allows watt-level continuous wave (cw) emission powers at room temperature. Moreover, narrow waveguides favor the fundamental TM00 lateral mode, resulting in a nearly Gaussian beam. To the extent that power efficiency is already largely optimized, power scaling in narrow-stripe QCLs is only possible through increasing the laser length, which is limited by the needs for robust construction and transparent antireflection coatings. Broad-area (BA) QCLs with a small number of cascades can also deliver watt-level cw powers at room temperature, profiting from the enhanced vertical heat flow. Power can be scaled for these lasers also via the laser width and is nearly unlimited. The usual drawback of the BA lasers is poor beam quality. We discuss the use of tapered QCLs and the first demonstration of room temperature cw operation of the BA QCL in fundamental TM00 mode. A stable and reproducible transverse optical mode is achieved using a double-taper waveguide geometry. The laser emits at 4.6  μm and has a demonstrated room temperature cw power of 100 mW.

© 2020 Society of Photo-Optical Instrumentation Engineers (SPIE) 0091-3286/2020/$28.00 © 2020 SPIE
Mykhaylo P. Semtsiv and William T. Masselink "Fundamental mode emission in tapered quantum cascade lasers for high brightness," Optical Engineering 59(8), 086101 (28 August 2020). https://doi.org/10.1117/1.OE.59.8.086101
Received: 25 February 2020; Accepted: 24 July 2020; Published: 28 August 2020
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KEYWORDS
Quantum cascade lasers

Waveguides

Continuous wave operation

Optical engineering

Gaussian beams

Resonators

Laser welding

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