Terahertz imaging and quantum cascade laser based devices

[摘要] (cont.) The challenges posed by the long THz wavelengths in QCL waveguide design leads to a tradeoff between high temperature operation (<186K) and high power/good beam patterns (248 mW peak, l2deg FWHM). To mitigate these tradeoffs, a technique for buttcoupling a metal-metal waveguide QCL to an index matched lens is developed. The resulting device achieves the highest reported power for a MM waveguide (145 mW peak) and while retaining a high operating temperature (160 K) and achieving a narrow beam pattern (<5deg). The lens coupling technique is also used to add spectroscopic capability to the system, through the development of an external cavity QCL. The butt-coupling of an antireflection coated lens to a semi-insulating surface plasmon waveguide QCL results in increased optical losses and suppression of lasing. Lasing is recovered using an external optical system with a reflective grating for frequency selective feedback. A device is characterized showing 4% tuning range at ~4.4 THz, and is among the first demonstrations of tunable THz QLCs.

[发布机构] Massachusetts Institute of Technology