Kumar, Jin and John L. Reno of Sandia are reporting another terahertz technology breakthrough: they have developed a new phase-locking technique for plasmonic lasers and, through its use, achieved a record-high power output for terahertz lasers. Their laser produced the highest radiative efficiency for any single-wavelength semiconductor quantum cascade laser. This is the first report of a radiative efficiency of greater than 50% achieved in such QCLs (quantum-cascade lasers).
Terahertz QCLs, which utilize optical cavities with metal coatings (claddings) for light confinement, are a class of lasers known as plasmonic lasers that are notorious for their poor radiative properties.
In 2018, Kumar reported on a simple yet effective technique to enhance the power output of single-mode lasers based on a new type of “distributed-feedback” mechanism.
Plasmonic lasers suffer from low output power and divergent beams due to their subwavelength metallic cavities. We developed a phase-locking scheme for such lasers to significantly enhance their radiative efficiency and beam quality. An array of metallic microcavities is longitudinally coupled through traveling plasmon waves, which leads to radiation in a single spectral mode and a diffraction limited single-lobed beam in the surface normal direction. We implemented our scheme for terahertz plasmonic quantum-cascade lasers (QCLs) and measured peak output power in excess of 2W for a single-mode 3.3THz QCL radiating in a narrow single-lobed beam, when operated at 58K in a compact Stirling cooler. We thereby demonstrated an order of magnitude increase in power and thirty-times higher average intensity for monolithic single-mode terahertz QCLs compared to prior work. The number of photons radiated from the cavity outnumber those absorbed within its claddings and semiconductor medium, which constitutes over 50% radiative efficiency and is significantly greater than that achieved for previous single-mode mid-infrared or terahertz QCLs.
SOURCES- Optica, Lehigh, Sandia
Written By Brian Wang, Nextbigfuture.com
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