Phase-locked terahertz plasmonic laser array with 2 W output power in a single spectral mode

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 2 W for a single-mode 3.3 THz QCL radiating in a narrow single-lobed beam, when operated at 58 K 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 >50% radiative efficiency and is significantly greater than that achieved for previous single-mode mid-infrared or terahertz QCLs. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement