Abstract-High-Q resonant cavities for terahertz quantum cascade lasers

High-Q resonant cavities for terahertz quantum cascade lasers A. Campa, L. Consolino, M. Ravaro, D. Mazzotti, M. S. Vitiello, S. Bartalini, and P. De Natale  »View Author Affiliations http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-3-3751

Optics Express, Vol. 23, Issue 3, pp. 3751-3761 (2015)
http://dx.doi.org/10.1364/OE.23.003751

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We report on the realization and characterization of two different designs for resonant THz cavities, based on wire-grid polarizers as input/output couplers, and injected by a continuous-wave quantum cascade laser (QCL) emitting at 2.55 THz. A comparison between the measured resonators parameters and the expected theoretical values is reported. With achieved quality factor Q ≈ 2.5 × 10⁵, these cavities show resonant peaks as narrow as few MHz, comparable with the typical Doppler linewidth of THz molecular transitions and slightly broader than the free-running QCL emission spectrum. The effects of the optical feedback from one cavity to the QCL are examined by using the other cavity as a frequency reference.

© 2015 Optical Society of America

Abstract-Continuous-wave coherent imaging with terahertz quantum cascade lasers using electro-optic harmonic sampling

M. Ravaro¹, V. Jagtap¹, G. Santarelli², C. Sirtori¹, L. H. Li³, S. P. Khanna³, E. H. Linfield³, and S. Barbieri¹

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¹Laboratoire Matériaux et Phénomènes Quantiques (MPQ) and CNRS, UMR 7162, Université Paris-Diderot, 10, rue A. Domont et L. Duquet, 75205 Paris, France
²Laboratoire Photonique, Numérique et Nanosciences (LP2N) and CNRS, UMR 5298, Université de Bordeaux 1, Institut d'Optique, 351 cours de la Libération, 33405 Talence, France
³School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom                        

We demonstrate a coherent imaging system based on a terahertz (THz) frequency quantum cascade laser (QCL) phase-locked to a near-infrared fs-laser comb. The phase locking enables coherent electro-optic sampling of the continuous-wave radiation emitted by the QCL through the generation of a heterodyne beat-note signal. We use this beat-note signal to demonstrate raster scan coherent imaging using a QCL emitting at 2.5 THz. At this frequency the detection noise floor of our system is of 3 pW/Hz and the long-term phase stability is <3°/h, limited by the mechanical stability of the apparatus.