Narrow-linewidth ultra-broadband terahertz sources based on difference-frequency generation in mid-infrared quantum cascade lasers
Authors: Jung S., Jiang Y., Kim J.H., Consolino L., Bartalini S., De Natale P., Vitello M., Fujita K., Hitaka M., Ito A., Kirch J., Botez D., Demmerle F., Boehm G., Amann M.-C., Belkin M.A.
Autors Affiliation: Department of Electrical and Computer Engineering, University of Texas at Austin, 10100 Burnet Road, Austin, TX 78758, United States; LENS, European Laboratory for NonLinear Spectroscopy, Via N. Carrara 1, Sesto Fiorentino (FI), I-50019, Italy; NEST, CNR- Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa, I-56127, Italy; Central Research Laboratory, Hamamatsu Photonics K.K., Hamakitaku, Hamamatsu, 434-8601, Japan; Department of Electrical and Computer Engineering, University of Wisconsin, Madison, WI 53706, United States; Walter Schottky Institut, Technische Universität München, Garching, 85748, Germany
Abstract: We discuss novel approaches to improve the tuning bandwidth and power output of terahertz (THz) sources based on difference-frequency generation (DFG) in mid-infrared quantum cascade lasers (QCLs). Using a double Littrow external-cavity system, we experimentally demonstrate that both doubly-resonant terms and optical rectification terms in the expression for the intersubband optical nonlinearity contribute to THz generation in DFG-QCLs and report THz DFG-QCLs with the optimized optical rectification terms. We also demonstrate a hybrid DFG-QCL device on silicon that enables significant improvement on THz out-coupling efficiency and results in more than 5 times higher THz output power compared to that of a reference device on its native semi-insulating InP substrate. Finally, we report for the first time the THz emission linewidth of a free-running continuous-wave THz DFG-QCL.
More Information: This work was supported by the National Science Foundation (NSF) with grants number ECCS-1150449 (CAREER), ECCS-1408511, and IIP-1448707 (SBIR), as well as by the Army Research Office (ARO) with grants number W911NF-15-1-0630 (STIR) and W911NF-16-C-0128 (STTR Phase II). M.A.B. acknowledges support by the Humboldt Foundation Wilhelm Bessel Research Award, J.H.K. acknowledges the support from Kwanjeong Educational Foundation (KEF) (12AmB06G). – The Society of Photo-Optical Instrumentation Engineers (SPIE)KeyWords: Infrared devices; Linewidth; Nonlinear optics; Optical frequency conversion; Quantum cascade lasers; Terahertz waves, Difference-frequency generation; Littrow external cavities; Mid-infrared quantum cascade; Nonlinear optical rectification; Optical nonlinearity; Optical rectifications; Out-coupling efficiency; Tera Hertz, Semiconductor lasersDOI: 10.1117/12.2256099