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

^{http://apl.aip.org/resource/1/applab/v102/i9/p091107_s1?isAuthorized=no}

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.