Abstract-Dual resonance phonon–photon–phonon terahertz quantum-cascade laser: physics of the electron transport and temperature performance optimization

 

Aleksandar Demić, Zoran Ikonić, Paul Dean, Dragan Indjin

Schematic diagram of effectively two (a), three (b,c) and four (d,e,f) level schemes of common THz QCL designs. The rectangles illustrate the typical wavefunction localisation (probability density) of each state within the QCL period. The dotted arrow line denotes the tunnelling process between two adjacent periods, while the solid arrow lines denote the transitions. Each level (apart from ULL) may be envisaged as a cluster of narrowly spaced quasi–bound levels, transitions between the effective "levels" also exist, however dominant mechanisms are shown.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-26-38788&id=444650

The state of the art terahertz-frequency quantum cascade lasers have opened a plethora of applications over the past two decades by testing several designs up to the very limit of operating temperature, optical power and lasing frequency performance. The temperature degradation mechanisms have long been under the debate for limiting the operation up to 210 K in pulsed operation in the GaAs/AlGaAs material system. In this work, we review the existing designs and exploit two main temperature degradation mechanisms by presenting a design in which they both prove beneficial to the lasing operation by dual pumping and dual extracting lasing levels. We have applied the density matrix transport model to select potential candidate structures by simulating over two million active region designs. We present several designs which offer better performance than the current record structure.

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.
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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.

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