From Event: SPIE Optical Engineering + Applications, 2017
Achieving high power in combination with high quality beam pattern is a ubiquitous challenge for semiconductor lasers. The demonstration of vertical-external-cavity surface-emitting lasers (VECSELs) in 1997 for visible and near-infrared semiconductor lasers has been a very successful approach. Terahertz (THz) quantum-cascade (QC) lasers, also have the challenge of combining high power and good beam pattern into one device – even more so because they typically use sub-wavelength metallic waveguides. The concept of VECSEL has been impossible to implement for QC lasers, since the optical gain is based on intersubband transitions of electrons, which only interact with the electric field polarized perpendicular to the quantum wells plane according to the "intersubband selection rule". To address this issue, we have developed an amplifying metasurface reflector that can couple the incident THz wave with the QC gain medium via metal-metal micro-cavity antenna reflectarray. Pairing the active metasurface with an output coupler, we demonstrated the first VECSEL in the THz regime in 2015. Based upon the prototype design, we have achieved a number of improvements to the QC-VECSEL including designing an inhomogeneous focusing metasurface to achieve a near-diffraction limited beam pattern with M2 = 1.3 and high brightness of 1.86×106 Wsr-1m-2, designing compact cavities and optimizing metasurface bias area to achieve continuous-wave operation above 77 K, achieving record high slope efficiency of 745 mW/A, as well as extending the VECSEL concept to cover a broad frequency range from 2.5 - 4.4 THz.
Luyao Xu, Christopher A. Curwen, Daguan Chen, John L. Reno, Tatsuo Itoh, and Benjamin S. Williams, "Terahertz metasurface quantum-cascade VECSEL (Conference Presentation)," Proc. SPIE 10383, Terahertz Emitters, Receivers, and Applications VIII, 1038306 (Presented at SPIE Optical Engineering + Applications: August 06, 2017; Published: 19 September 2017); https://doi.org/10.1117/12.2273447.5581158791001.
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