Low-Power-Consumption, Single-Mode Quantum Cascade Lasers Fabricated Without Epitaxial Regrowth

Quantum cascade (QC) lasers employ intersubband electronic transitions in semiconductor quantum well structures to generate emission at specific engineered wavelengths. QC devices have been particularly successful as mid-infrared emitters in the 4- to 12-μm wavelength range, a spectral regime that is difficult to access with interband diode lasers. As cascade devices, QC lasers can also be designed with many gain stages, which, combined with optimized doping and optical design, has enabled the development of lasers with remarkably high continuous output power (in excess of 1 W). One of the most important applications of mid-infrared QC lasers is quantitative gas detection using absorption spectroscopy, where a single-frequency laser is used to interrogate specific absorption lines of a target compound. While high output power is essential in certain applications, many in situ absorption spectrometers require only milliwatt-level output to effectively measure low levels of compounds of interest with strong absorption lines in the mid-infrared regime.