Abstract-Multi-spectral terahertz sensing: proposal for a coupled-cavity quantum cascade laser based optical feedback interferometer

Xiaoqiong Qi, Gary Agnew, Iman Kundu, Thomas Taimre, Yah Leng Lim, Karl Bertling, Paul Dean, Andrew Grier, Alexander Valavanis, Edmund H. Linfield, A. Giles Davies, Dragan Indjin, and Aleksandar D. Rakić

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-9-10153

We propose a laser feedback interferometer operating at multiple terahertz (THz) frequency bands by using a pulsed coupled-cavity THz quantum cascade laser (QCL) under optical feedback. A theoretical model that contains multi-mode reduced rate equations and thermal equations is presented, which captures the interplay between electro-optical, thermal, and feedback effects. By using the self-heating effect in both active and passive cavities, self-mixing signal responses at three different THz frequency bands are predicted. A multi-spectral laser feedback interferometry system based on such a coupled-cavity THz QCL will permit ultra-high-speed sensing and spectroscopic applications including material identification.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-Optical feedback effects on terahertz quantum cascade lasers: modelling and applications

Aleksandar D. Rakić, Yah Leng Lim, Thomas Taimre, Gary Agnew, Xiaoqiong Qi, Karl Bertling, She Han, Stephen J. Wilson

The Univ. of Queensland (Australia)

Andrew Grier, Zoran Ikonić, Alexander Valavanis, Aleksandar Demić, James Keeley, Lianhe H. Li, Edmund H. Linfield, A. Giles Davies, Dragan Indjin

Univ. of Leeds (United Kingdom)

Paul Harrison

Sheffield Hallam Univ. (United Kingdom)

Blake Ferguson, Graeme Walker

QIMR Berghofer Medical Research Institute (Australia)

Tarl W. Prow, H. Peter Soyer

The Univ. of Queensland School of Medicine (Australia)

Proc. SPIE 10030, Infrared, Millimeter-Wave, and Terahertz Technologies IV, 1003016 (December 8, 2016); doi:10.1117/12.2250621

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2593076






Terahertz (THz) quantum cascade lasers (QCLs) are compact sources of radiation in the 1–5 THz range with significant potential for applications in sensing and imaging. Laser feedback interferometry (LFI) with THz QCLs is a technique utilizing the sensitivity of the QCL to the radiation reflected back into the laser cavity from an external target. We will discuss modelling techniques and explore the applications of LFI in biological tissue imaging and will show that the confocal nature of the QCL in LFI systems, with their innate capacity for depth sectioning, makes them suitable for skin diagnostics with the well-known advantages of more conventional confocal microscopes. A demonstration of discrimination of neoplasia from healthy tissue using a THz, LFI-based system in the context of melanoma is presented using a transgenic mouse model.
 © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Model for a pulsed terahertz quantum cascade laser under optical feedback

Gary Agnew, Andrew Grier, Thomas Taimre, Yah Leng Lim, Karl Bertling, Zoran Ikonić, Alexander Valavanis, Paul Dean, Jonathan Cooper, Suraj P. Khanna, Mohammad Lachab, Edmund H. Linfield, A. Giles Davies, Paul Harrison, Dragan Indjin, and Aleksandar D. Rakić

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-18-20554

Optical feedback effects in lasers may be useful or problematic, depending on the type of application. When semiconductor lasers are operated using pulsed-mode excitation, their behavior under optical feedback depends on the electronic and thermal characteristics of the laser, as well as the nature of the external cavity. Predicting the behavior of a laser under both optical feedback and pulsed operation therefore requires a detailed model that includes laser-specific thermal and electronic characteristics. In this paper we introduce such a model for an exemplar bound-to-continuum terahertz frequency quantum cascade laser (QCL), illustrating its use in a selection of pulsed operation scenarios. Our results demonstrate significant interplay between electro-optical, thermal, and feedback phenomena, and that this interplay is key to understanding QCL behavior in pulsed applications. Further, our results suggest that for many types of QCL in interferometric applications, thermal modulation via low duty cycle pulsed operation would be an alternative to commonly used adiabatic modulation.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Full Article  |  PDF Article