Abstract-Coherent imaging using laser feedback interferometry with pulsed-mode terahertz quantum cascade lasers

Yah Leng Lim, Karl Bertling, Thomas Taimre, Tim Gillespie, Chris Glenn, Ashley Robinson, Dragan Indjin, Yingjun Han, Lianhe Li, Edmund H. Linfield, A. Giles Davies, Paul Dean, and Aleksandar D. Rakić

Fig. 1 (a) Schematic diagram of the experimental setup. (b) Expanded view of the QCL cold finger module. (c) Photo of the THz QCL mounted on the cold finger of the Stirling cooler.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-7-10221

We report a coherent terahertz (THz) imaging system that utilises a quantum cascade laser (QCL) operating in pulsed-mode as both the source and detector. The realisation of a short-pulsed THz QCL feedback interferometer permits both high peak powers and improved thermal efficiency, which enables the cryogen-free operation of the system. In this work, we demonstrated pulsed-mode swept-frequency laser feedback interferometry experimentally. Our interferometric detection scheme not only permits the simultaneous creation of both amplitude and phase images, but inherently suppresses unwanted background radiation. We demonstrate that the proposed system utilising microsecond pulses has the potential to achieve 0.25 mega-pixel per second acquisition rates, paving the pathway to video frame rate THz imaging.

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-Measurement of the emission spectrum of a semiconductor laser using laser-feedback interferometry

• James Keeley, 
• Joshua Freeman, 
• Karl Bertling, 
• Yah L. Lim, 
• Reshma A. Mohandas, 
• Thomas Taimre, 
• Lianhe H. Li, 
• Dragan Indjin, 
• Aleksandar D. Rakić, 
• Edmund H. Linfield, 
• A. Giles Davies & 
• Paul Dean

https://www.nature.com/articles/s41598-017-07432-0?WT.feed_name=subjects_chemistry

The effects of optical feedback (OF) in lasers have been observed since the early days of laser development. While OF can result in undesirable and unpredictable operation in laser systems, it can also cause measurable perturbations to the operating parameters, which can be harnessed for metrological purposes. In this work we exploit this ‘self-mixing’ effect to infer the emission spectrum of a semiconductor laser using a laser-feedback interferometer, in which the terminal voltage of the laser is used to coherently sample the reinjected field. We demonstrate this approach using a terahertz frequency quantum cascade laser operating in both single- and multiple-longitudinal mode regimes, and are able to resolve spectral features not reliably resolved using traditional Fourier transform spectroscopy. We also investigate quantitatively the frequency perturbation of individual laser modes under OF, and find excellent agreement with predictions of the excess phase equation central to the theory of lasers under OF.

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-Methodology for materials analysis using swept-frequency feedback interferometry with terahertz frequency quantum cascade lasers

Thomas Taimre, Karl Bertling, Yah Leng Lim, Paul Dean, Dragan Indjin, and Aleksandar D. Rakić  »View Author Affiliations

Optics Express, Vol. 22, Issue 15, pp. 18633-18647 (2014)

Recently, we demonstrated an interferometric materials analysis scheme at terahertz frequencies based on the self-mixing effect in terahertz quantum cascade lasers. Here, we examine the impact of variations in laser operating parameters, target characteristics, laser–target system properties, and the quality calibration standards on our scheme. We show that our coherent scheme is intrinsically most sensitive to fluctuations in interferometric phase, arising primarily from variations in external cavity length. Moreover we demonstrate that the smallest experimental uncertainties in the determination of extinction coefficients are expected for lossy materials.

© 2014 Optical Society of America