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

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

http://espace.library.uq.edu.au/view/UQ:353012

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.