Abstract-Optomechanical response with nanometer resolution in the self-mixing signal of a terahertz quantum cascade laser

Andrea Ottomaniello, James Keeley, Pierluigi Rubino, Lianhe Li, Marco Cecchini, Edmund H. Linfield, A. Giles Davies, Paul Dean, Alessandro Pitanti, Alessandro Tredicucci,

(a) Sketch of the two configurations of the SM apparatus. (b) Calculated Δ𝑁$\mathrm{\Delta }N$ (blue curve), and measured 𝑉SM$V_{\mathrm{S}\mathrm{M}}$ (red points) as a function of Δ𝐿$\mathrm{\Delta }L$ using configuration 1

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-23-5663

Owing to their intrinsic stability against optical feedback (OF), quantum cascade lasers (QCLs) represent a uniquely versatile source to further improve self-mixing interferometry at mid-infrared and terahertz (THz) frequencies. Here, we show the feasibility of detecting with nanometer precision, the deeply subwavelength (<𝜆/6000$<\lambda /6000$) mechanical vibrations of a suspended Si3N4${\mathrm{S}\mathrm{i}}_3{\mathrm{N}}_4$ membrane used as the external element of a THz QCL feedback interferometer. Besides representing an extension of the applicability of vibrometric characterization at THz frequencies, our system can be exploited for the realization of optomechanical applications, such as dynamical switching between different OF regimes and a still-lacking THz master-slave configuration.

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-Coherent three-dimensional terahertz imaging through self-mixing in a quantum cascade laser

Paul Dean^1,a), Alex Valavanis¹, James Keeley¹, Karl Bertling², Yah Leng Lim²,Raed Alhathlool¹, Siddhant Chowdhury¹, Thomas Taimre³, Lianhe H. Li¹,Dragan Indjin¹, Stephen J. Wilson², Aleksandar D. Rakić², Edmund H. Linfield¹ and A. Giles Davies¹
^{http://scitation.aip.org/content/aip/journal/apl/103/18/10.1063/1.4827886}

1 School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
2 School of Information Technology and Electrical Engineering, The University of Queensland, St. Lucia, Queensland 4072, Australia
3 School of Mathematics and Physics, The University of Queensland, St. Lucia, Queensland 4072, Australia

We demonstrate coherent terahertz (THz) frequency imaging using the self-mixing effect in aquantum cascade laser (QCL). Self-mixing voltage waveforms are acquired at each pixel of a two-dimensional image of etched GaAs structures and fitted to a three-mirror laser model, enabling extraction of the amplitude and phase parameters of the reflected field. From the phase, wereconstruct the depth of the sample surface, and we show that the amplitude can be related to the sample reflectance. Our approach is experimentally simple and compact, and does not require frequency stabilization of the THz QCL.