Abstract-Active phase-nulling of the self-mixing phase in a terahertz frequency quantum cascade laser

Active phase-nulling of the self-mixing phase in a terahertz frequency quantum cascade laser P. Dean, J. Keeley, A. Valavanis, K. Bertling, Y. L. Lim, T. Taimre, R. Alhathlool, L. H. Li, D. Indjin, A. D. Rakić, E. H. Linfield, and A. G. Davies  »View Author Affiliations

Optics Letters, Vol. 40, Issue 6, pp. 950-953 (2015)
http://dx.doi.org/10.1364/OL.40.000950

View Full Text Article

Enhanced HTML    Acrobat PDF (432 KB) 

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-40-6-950

We demonstrate an active phase-nulling scheme for terahertz (THz) frequency quantum cascade lasers (QCLs) under optical feedback, by active electronic feedback control of the emission frequency. Using this scheme, the frequency tuning rate of a THz QCL is characterized, with significantly reduced experimental complexity compared to alternative approaches. Furthermore, we demonstrate real-time displacement sensing of targets, overcoming the resolution limits imposed by quantization in previously implemented fringe-counting methods. Our approach is readily applicable to high-frequency vibrometry and surface profiling of targets, as well as frequency-stabilization schemes for THz QCLs.

© 2015 Optical Society of America

Abstract- Three-dimensional terahertz imaging using swept-frequency feedback interferometry with a quantum cascade laser

Three-dimensional terahertz imaging using swept-frequency feedback interferometry with a quantum cascade laser

J. Keeley, P. Dean, A. Valavanis, K. Bertling, Y. L. Lim, R. Alhathlool, T. Taimre, L. H. Li, D. Indjin, A. D. Rakić, E. H. Linfield, and A. G. Davies  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-40-6-994

Optics Letters, Vol. 40, Issue 6, pp. 994-997 (2015)
http://dx.doi.org/10.1364/OL.40.000994

View Full Text Article

Enhanced HTML    Acrobat PDF (488 KB)

We demonstrate coherent three-dimensional terahertz imaging by frequency modulation of a quantum cascade laser in a compact and experimentally simple self-mixing scheme. Through this approach, we can realize significantly faster acquisition rates compared to previous schemes employing longitudinal mechanical scanning of a sample. We achieve a depth resolution of better than 0.1 μm with a power noise spectral density below −50  dB/Hz, for a sampling time of 10  ms/pixel.

© 2015 Optical Society of America