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Qi X, Bertling K, Torniainen J, Kong F, Gillespie T, Primiero C, Stark MS, Dean P, Indjin D, Li LH, Linfield EH, Davies AG, Brünig M, Mills T, Rosendahl C, Soyer HP, Rakić AD. Terahertz in vivo imaging of human skin: Toward detection of abnormal skin pathologies. APL Bioeng 2024; 8:016117. [PMID: 38476403 PMCID: PMC10932572 DOI: 10.1063/5.0190573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Accepted: 02/19/2024] [Indexed: 03/14/2024] Open
Abstract
Terahertz (THz) imaging has long held promise for skin cancer detection but has been hampered by the lack of practical technological implementation. In this article, we introduce a technique for discriminating several skin pathologies using a coherent THz confocal system based on a THz quantum cascade laser. High resolution in vivo THz images (with diffraction limited to the order of 100 μm) of several different lesion types were acquired and compared against one another using the amplitude and phase values. Our system successfully separated pathologies using a combination of phase and amplitude information and their respective surface textures. The large scan field (50 × 40 mm) of the system allows macroscopic visualization of several skin lesions in a single frame. Utilizing THz imaging for dermatological assessment of skin lesions offers substantial additional diagnostic value for clinicians. THz images contain information complementary to the information contained in the conventional digital images.
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Affiliation(s)
- X. Qi
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - K. Bertling
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - J. Torniainen
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - F. Kong
- Dermatology Research Centre, Frazer Institute, The University of Queensland, Woolloongabba QLD 4102, Australia
| | - T. Gillespie
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - C. Primiero
- Dermatology Research Centre, Frazer Institute, The University of Queensland, Woolloongabba QLD 4102, Australia
| | - M. S. Stark
- Dermatology Research Centre, Frazer Institute, The University of Queensland, Woolloongabba QLD 4102, Australia
| | - P. Dean
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - D. Indjin
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - L. H. Li
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - E. H. Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - A. G. Davies
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - M. Brünig
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
| | - T. Mills
- OscillaDx Pty Ltd, Brisbane, Queensland, Australia
| | - C. Rosendahl
- General Practice Clinical Unit, Faculty of Medicinee, The University of Queensland, Herston QLD 4029, Australia
| | - H. P. Soyer
- Dermatology Research Centre, Frazer Institute, The University of Queensland, Woolloongabba QLD 4102, Australia
| | - A. D. Rakić
- School of Electrical Engineering and Computer Science, The University of Queensland, Brisbane QLD 4072, Australia
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2
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Vaughan M, Michailow W, Salih M, Li L, Beere H, Ritchie DA, Linfield EH, Davies AG, Cunningham JE. Directed delivery of terahertz frequency radiation from quantum cascade lasers within a dry 3He dilution refrigerator. Rev Sci Instrum 2022; 93:113906. [PMID: 36461439 DOI: 10.1063/5.0102553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 10/08/2022] [Indexed: 06/17/2023]
Abstract
We present a scheme for the full integration of terahertz (THz) frequency quantum cascade lasers (QCLs) within a dilution refrigerator in order to provide a directed delivery of THz power into the sample space. We describe a successful operation of a 2.68 THz QCL located on the pulse tube cooler stage of the refrigerator, with its output coupled onto a two-dimensional electron gas (2DEG) located on a milli-kelvin sample stage via hollow metal waveguides and Hysol thermal isolators, achieving a total loss from QCL to the sample of ∼-9 dB. The thermal isolators limit heat leaks to the sample space, with a base temperature of ∼210 mK being achieved. We observe cyclotron resonance (CR) induced in the 2DEG by the QCL and explore the heating impact of the QCL on all stages of the refrigerator. The CR effect induced by the THz QCL is observable at electron temperatures as low as ∼430 mK. The results show a viable route for the exploitation of THz QCLs within the environment of a dilution refrigerator and for the THz power delivery in very low-temperature (<0.5 K) condensed matter experiments.
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Affiliation(s)
- M Vaughan
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, West Yorkshire LS2 9JT, United Kingdom
| | - W Michailow
- Cavendish Laboratory, University of Cambridge, Cambridge, Cambridgeshire CB3 0HE, United Kingdom
| | - M Salih
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, West Yorkshire LS2 9JT, United Kingdom
| | - L Li
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, West Yorkshire LS2 9JT, United Kingdom
| | - H Beere
- Cavendish Laboratory, University of Cambridge, Cambridge, Cambridgeshire CB3 0HE, United Kingdom
| | - D A Ritchie
- Cavendish Laboratory, University of Cambridge, Cambridge, Cambridgeshire CB3 0HE, United Kingdom
| | - E H Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, West Yorkshire LS2 9JT, United Kingdom
| | - A G Davies
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, West Yorkshire LS2 9JT, United Kingdom
| | - J E Cunningham
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, West Yorkshire LS2 9JT, United Kingdom
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3
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Riepl J, Raab J, Abajyan P, Nong H, Freeman JR, Li LH, Linfield EH, Davies AG, Wacker A, Albes T, Jirauschek C, Lange C, Dhillon SS, Huber R. Field-resolved high-order sub-cycle nonlinearities in a terahertz semiconductor laser. Light Sci Appl 2021; 10:246. [PMID: 34924564 PMCID: PMC8685277 DOI: 10.1038/s41377-021-00685-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 11/18/2021] [Accepted: 11/23/2021] [Indexed: 06/14/2023]
Abstract
The exploitation of ultrafast electron dynamics in quantum cascade lasers (QCLs) holds enormous potential for intense, compact mode-locked terahertz (THz) sources, squeezed THz light, frequency mixers, and comb-based metrology systems. Yet the important sub-cycle dynamics have been notoriously difficult to access in operational THz QCLs. Here, we employ high-field THz pulses to perform the first ultrafast two-dimensional spectroscopy of a free-running THz QCL. Strong incoherent and coherent nonlinearities up to eight-wave mixing are detected below and above the laser threshold. These data not only reveal extremely short gain recovery times of 2 ps at the laser threshold, they also reflect the nonlinear polarization dynamics of the QCL laser transition for the first time, where we quantify the corresponding dephasing times between 0.9 and 1.5 ps with increasing bias currents. A density-matrix approach reproducing the emergence of all nonlinearities and their ultrafast evolution, simultaneously, allows us to map the coherently induced trajectory of the Bloch vector. The observed high-order multi-wave mixing nonlinearities benefit from resonant enhancement in the absence of absorption losses and bear potential for a number of future applications, ranging from efficient intracavity frequency conversion, mode proliferation to passive mode locking.
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Affiliation(s)
- J Riepl
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - J Raab
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - P Abajyan
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France
| | - H Nong
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France
| | - J R Freeman
- School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds, UK
| | - L H Li
- School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds, UK
| | - E H Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds, UK
| | - A G Davies
- School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds, UK
| | - A Wacker
- Mathematical Physics and NanoLund, Lund University, Lund, Sweden
| | - T Albes
- Department of Electrical and Computer Engineering, Technical University of Munich, Munich, Germany
| | - C Jirauschek
- Department of Electrical and Computer Engineering, Technical University of Munich, Munich, Germany
| | - C Lange
- Department of Physics, TU Dortmund University, Dortmund, Germany
| | - S S Dhillon
- Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France.
| | - R Huber
- Department of Physics, University of Regensburg, Regensburg, Germany
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4
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Park SJ, Zonetti S, Parker-Jervis RS, Wu J, Wood CD, Li LH, Davies AG, Linfield EH, Sydoruk O, Cunningham JE. Terahertz magnetoplasmon resonances in coupled cavities formed in a gated two-dimensional electron gas. Opt Express 2021; 29:12958-12966. [PMID: 33985041 DOI: 10.1364/oe.414178] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Accepted: 03/11/2021] [Indexed: 06/12/2023]
Abstract
We report on both experiments and theory of low-terahertz frequency range (up to 400 GHz) magnetoplasmons in a gated two-dimensional electron gas at low (<4K) temperatures. The evolution of magnetoplasmon resonances was observed as a function of magnetic field at frequencies up to ∼400 GHz. Full-wave 3D simulations of the system predicted the spatial distribution of plasmon modes in the 2D channel, along with their frequency response, allowing us to distinguish those resonances caused by bulk and edge magnetoplasmons in the experiments. Our methodology is anticipated to be applicable to the low temperature (<4K) on-chip terahertz measurements of a wide range of other low-dimensional mesoscopic systems.
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Kundu I, Freeman JR, Dean P, Li LH, Linfield EH, Davies AG. Terahertz photonic integrated circuit for frequency tuning and power modulation. Opt Express 2020; 28:4374-4386. [PMID: 32121675 DOI: 10.1364/oe.380656] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Accepted: 01/10/2020] [Indexed: 06/10/2023]
Abstract
The quantum cascade laser is a powerful solid-state source of terahertz-frequency radiation. However, integrating multiple photonic functions into a monolithic platform in this frequency range is non-trivial due to the scaling of photonic structures for the long terahertz wavelengths and the low frequency tuning coefficients of the quantum cascade lasers. Here, we have designed a simple terahertz-frequency photonic integrated circuit by coupling a racetrack resonator with a ridge laser in the longitudinal direction to design a notch filter. The transmission properties of this filter structure are dependent on the phase matching and losses in the coupled racetrack and results in a comb of stopband frequencies. We have optimized the comb separation by carefully selecting the cavity dimensions of the racetrack resonator to suppress longitudinal modes in the ridge laser enabling single-mode emission. The emission frequencies and output power from laser are controlled through appropriate control of drive currents to the ridge and the racetrack resonator. The emission frequency is electrically tuned over ∼81 GHz exploiting Stark shift of the gain as a function of drive current at the ridge laser, coinciding with an output power variation of ∼27% of the peak power (at a heat sink temperature of 50 K). The output power from the ridge also varied by ∼30% and the frequency was tuned by a further 10 GHz when the driving conditions at the ridge laser are invariant and the current at the racetrack resonator was varied. To our best knowledge, this is the first report of a frequency engineering, tuning and power modulation of terahertz-frequency quantum cascade lasers using a photonic integrated circuit.
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6
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Meng K, Park SJ, Li LH, Bacon DR, Chen L, Chae K, Park JY, Burnett AD, Linfield EH, Davies AG, Cunningham JE. Tunable broadband terahertz polarizer using graphene-metal hybrid metasurface. Opt Express 2019; 27:33768-33778. [PMID: 31878438 DOI: 10.1364/oe.27.033768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Accepted: 10/14/2019] [Indexed: 06/10/2023]
Abstract
We demonstrate an electrically tunable polarizer for terahertz (THz) frequency electromagnetic waves formed from a hybrid graphene-metal metasurface. Broadband (>3 THz) polarization-dependent modulation of THz transmission is demonstrated as a function of the graphene conductivity for various wire grid geometries, each tuned by gating using an overlaid ion gel. We show a strong enhancement of modulation (up to ∼17 times) compared to graphene wire grids in the frequency range of 0.2-2.5 THz upon introduction of the metallic elements. Theoretical calculations, considering both plasmonic coupling and Drude absorption, are in good agreement with our experimental findings.
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7
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Houver S, Lebreton A, Pereira TAS, Xu G, Colombelli R, Kundu I, Li LH, Linfield EH, Davies AG, Mangeney J, Tignon J, Ferreira R, Dhillon SS. Giant optical nonlinearity interferences in quantum structures. Sci Adv 2019; 5:eaaw7554. [PMID: 31828223 PMCID: PMC6890450 DOI: 10.1126/sciadv.aaw7554] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Accepted: 09/09/2019] [Indexed: 06/10/2023]
Abstract
Second-order optical nonlinearities can be greatly enhanced by orders of magnitude in resonantly excited nanostructures. These resonant nonlinearities continually attract attention, particularly in newly discovered materials. However, they are frequently not as heightened as currently predicted, limiting their exploitation in nanostructured nonlinear optics. Here, we present a clear-cut theoretical and experimental demonstration that the second-order nonlinear susceptibility can vary by orders of magnitude as a result of giant destructive, as well as constructive, interference effects in complex systems. Using terahertz quantum cascade lasers as a model source to investigate interband and intersubband nonlinearities, we show that these giant interferences are a result of an unexpected interplay of the second-order nonlinear contributions of multiple light and heavy hole states. As well as of importance to understand and engineer the resonant optical properties of nanostructures, this advanced framework can be used as a novel, sensitive tool to elucidate the band structure properties of complex materials.
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Affiliation(s)
- S. Houver
- Laboratoire de Physique de l’Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France
| | - A. Lebreton
- Laboratoire de Physique de l’Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France
| | - T. A. S. Pereira
- Instituto de Física, Universidade Federal de Mato Grosso, 78060-900 Cuiabá, Mato Grosso, Brazil
| | - G. Xu
- Centre de Nanosciences et de Nanotechnologies, CNRS UMR 9001, Univ. Paris-Sud, Université Paris-Saclay, C2N-Orsay, 91405 Orsay, Cedex, France
| | - R. Colombelli
- Centre de Nanosciences et de Nanotechnologies, CNRS UMR 9001, Univ. Paris-Sud, Université Paris-Saclay, C2N-Orsay, 91405 Orsay, Cedex, France
| | - I. Kundu
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - L. H. Li
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - E. H. Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - A. G. Davies
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK
| | - J. Mangeney
- Laboratoire de Physique de l’Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France
| | - J. Tignon
- Laboratoire de Physique de l’Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France
| | - R. Ferreira
- Laboratoire de Physique de l’Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France
| | - S. S. Dhillon
- Laboratoire de Physique de l’Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France
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8
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Meng K, Park SJ, Burnett AD, Gill T, Wood CD, Rosamond M, Li LH, Chen L, Bacon DR, Freeman JR, Dean P, Ahn YH, Linfield EH, Davies AG, Cunningham JE. Increasing the sensitivity of terahertz split ring resonator metamaterials for dielectric sensing by localized substrate etching. Opt Express 2019; 27:23164-23172. [PMID: 31510599 DOI: 10.1364/oe.27.023164] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Accepted: 06/11/2019] [Indexed: 05/18/2023]
Abstract
We demonstrate a significant enhancement in the sensitivity of split ring resonator terahertz metamaterial dielectric sensors by the introduction of etched trenches into their inductive-capacitive gap area, both through finite element simulations and in experiments performed using terahertz time-domain spectroscopy. The enhanced sensitivity is demonstrated by observation of an increased frequency shift in response to overlaid dielectric material of thicknesses up to 18 µm deposited on to the sensor surface. We show that sensitivity to the dielectric is enhanced by a factor of up to ∼2.7 times by the incorporation of locally etched trenches with a depth of ∼3.4 µm, for example, and discuss the effect of the etching on the electrical properties of the sensors. Our experimental findings are in good agreement with simulations of the sensors obtained using finite element methods.
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Keeley J, Bertling K, Rubino PL, Lim YL, Taimre T, Qi X, Kundu I, Li LH, Indjin D, Rakić AD, Linfield EH, Davies AG, Cunningham J, Dean P. Detection sensitivity of laser feedback interferometry using a terahertz quantum cascade laser. Opt Lett 2019; 44:3314-3317. [PMID: 31259948 DOI: 10.1364/ol.44.003314] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Accepted: 05/08/2019] [Indexed: 06/09/2023]
Abstract
We report on the high detection sensitivity of a laser feedback interferometry scheme based on a terahertz frequency quantum cascade laser (QCL). We show that variations on the laser voltage induced by optical feedback to the laser can be resolved with the reinjection of powers as low as ∼-125 dB of the emitted power. Our measurements demonstrate a noise equivalent power of ∼1.4 pW/√Hz, although, after accounting for the reinjection losses, we estimate that this corresponds to only ∼1 fW/√Hz being coupled to the QCL active region.
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10
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Han YJ, Partington J, Chhantyal-Pun R, Henry M, Auriacombe O, Rawlings T, Li LH, Keeley J, Oldfield M, Brewster N, Dong R, Dean P, Davies AG, Ellison BN, Linfield EH, Valavanis A. Gas spectroscopy through multimode self-mixing in a double-metal terahertz quantum cascade laser. Opt Lett 2018; 43:5933-5936. [PMID: 30547973 DOI: 10.1364/ol.43.005933] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Accepted: 10/10/2018] [Indexed: 06/09/2023]
Abstract
A multimode self-mixing terahertz-frequency gas absorption spectroscopy is demonstrated based on a quantum cascade laser. A double-metal device configuration is used to expand the laser's frequency tuning range, and a precision-micromachined external waveguide module is used to enhance the optical feedback. Methanol spectra are measured using two laser modes at 3.362 and 3.428 THz, simultaneously, with more than eight absorption peaks resolved over a 17 GHz bandwidth, which provide the noise-equivalent absorption sensitivity of 1.20×10-3 cm-1 Hz-1/2 and 2.08×10-3 cm-1 Hz-1/2, respectively. In contrast to all previous self-mixing spectroscopy, our multimode technique expands the sensing bandwidth and duty cycle significantly.
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Han YJ, Li LH, Zhu J, Valavanis A, Freeman JR, Chen L, Rosamond M, Dean P, Davies AG, Linfield EH. Silver-based surface plasmon waveguide for terahertz quantum cascade lasers. Opt Express 2018; 26:3814-3827. [PMID: 29475360 DOI: 10.1364/oe.26.003814] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Accepted: 12/18/2017] [Indexed: 06/08/2023]
Abstract
Terahertz-frequency quantum cascade lasers (THz QCLs) based on ridge waveguides incorporating silver waveguide layers have been investigated theoretically and experimentally, and compared with traditional gold-based devices. The threshold gain associated with silver-, gold- and copper-based devices, and the effects of titanium adhesion layers and top contact layers, in both surface-plasmon and double-metal waveguide geometries, have been analysed. Our simulations show that silver-based waveguides yield lower losses for THz QCLs across all practical operating temperatures and frequencies. Experimentally, QCLs with silver-based surface-plasmon waveguides were found to exhibit higher operating temperatures and higher output powers compared to those with identical but gold-based waveguides. Specifically, for a three-well resonant phonon active region with a scaled oscillator strength of 0.43 and doping density of 6.83 × 1015 cm-3, an increase of 5 K in the maximum operating temperature and 40% increase in the output power were demonstrated. These effects were found to be dependent on the active region design, and greater improvements were observed for QCLs with a larger radiative diagonality. Our results indicate that silver-based waveguide structures could potentially enable THz QCLs to operate at high temperatures.
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12
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Han YJ, Li LH, Grier A, Chen L, Valavanis A, Zhu J, Freeman JR, Isac N, Colombelli R, Dean P, Davies AG, Linfield EH. Extraction-controlled terahertz frequency quantum cascade lasers with a diagonal LO-phonon extraction and injection stage. Opt Express 2016; 24:28583-28593. [PMID: 27958502 DOI: 10.1364/oe.24.028583] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We report an extraction-controlled terahertz (THz)-frequency quantum cascade laser design in which a diagonal LO-phonon scattering process is used to achieve efficient current injection into the upper laser level of each period and simultaneously extract electrons from the adjacent period. The effects of the diagonality of the radiative transition are investigated, and a design with a scaled oscillator strength of 0.45 is shown experimentally to provide the highest temperature performance. A 3.3 THz device processed into a double-metal waveguide configuration operated up to 123 K in pulsed mode, with a threshold current density of 1.3 kA/cm2 at 10 K. The QCL structures are modeled using an extended density matrix approach, and the large threshold current is attributed to parasitic current paths associated with the upper laser levels. The simplicity of this design makes it an ideal platform to investigate the scattering injection process.
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Baillergeau M, Maussang K, Nirrengarten T, Palomo J, Li LH, Linfield EH, Davies AG, Dhillon S, Tignon J, Mangeney J. Diffraction-limited ultrabroadband terahertz spectroscopy. Sci Rep 2016; 6:24811. [PMID: 27142959 PMCID: PMC4855139 DOI: 10.1038/srep24811] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Accepted: 04/05/2016] [Indexed: 11/09/2022] Open
Abstract
Diffraction is the ultimate limit at which details of objects can be resolved in conventional optical spectroscopy and imaging systems. In the THz spectral range, spectroscopy systems increasingly rely on ultra-broadband radiation (extending over more 5 octaves) making a great challenge to reach resolution limited by diffraction. Here, we propose an original easy-to-implement wavefront manipulation concept to achieve ultrabroadband THz spectroscopy system with diffraction-limited resolution. Applying this concept to a large-area photoconductive emitter, we demonstrate diffraction-limited ultra-broadband spectroscopy system up to 14.5 THz with a dynamic range of 10(3). The strong focusing of ultrabroadband THz radiation provided by our approach is essential for investigating single micrometer-scale objects such as graphene flakes or living cells, and besides for achieving intense ultra-broadband THz electric fields.
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Affiliation(s)
- M Baillergeau
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France
| | - K Maussang
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France
| | - T Nirrengarten
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France
| | - J Palomo
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France
| | - L H Li
- School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds LS29JT, UK
| | - E H Linfield
- School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds LS29JT, UK
| | - A G Davies
- School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds LS29JT, UK
| | - S Dhillon
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France
| | - J Tignon
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France
| | - J Mangeney
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France
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14
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Wang F, Kundu I, Chen L, Li L, Linfield EH, Davies AG, Moumdji S, Colombelli R, Mangeney J, Tignon J, Dhillon SS. Engineered far-fields of metal-metal terahertz quantum cascade lasers with integrated planar horn structures. Opt Express 2016; 24:2174-2182. [PMID: 26906793 DOI: 10.1364/oe.24.002174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The far-field emission profile of terahertz quantum cascade lasers (QCLs) in metal-metal waveguides is controlled in directionality and form through planar horn-type shape structures, whilst conserving a broad spectral response. The structures produce a gradual change in the high modal confinement of the waveguides and permit an improved far-field emission profile and resulting in a four-fold increase in the emitted output power. The two-dimensional far-field patterns are measured at 77 K and are agreement in with 3D modal simulations. The influence of parasitic high-order transverse modes is shown to be controlled by engineering the horn structure (ridge and horn widths), allowing only the fundamental mode to be coupled out.
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15
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Lao YF, Perera AGU, Li LH, Khanna SP, Linfield EH, Zhang YH, Wang TM. Mid-infrared photodetectors operating over an extended wavelength range up to 90 K. Opt Lett 2016; 41:285-288. [PMID: 26766695 DOI: 10.1364/ol.41.000285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report a wavelength threshold extension, from the designed value of 3.1 to 8.9 μm, in a p-type heterostructure photodetector. This is associated with the use of a graded barrier and barrier offset, and arises from hole-hole interactions in the detector absorber. Experiments show that using long-pass filters to tune the energies of incident photons gives rise to changes in the intensity of the response. This demonstrates an alternative approach to achieving tuning of the photodetector response without the need to adjust the characteristic energy that is determined by the band structure.
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16
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Keeley J, Dean P, Valavanis A, Bertling K, Lim YL, Alhathlool R, Taimre T, Li LH, Indjin D, Rakić AD, Linfield EH, Davies AG. Three-dimensional terahertz imaging using swept-frequency feedback interferometry with a quantum cascade laser. Opt Lett 2015; 40:994-997. [PMID: 25768165 DOI: 10.1364/ol.40.000994] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We demonstrate coherent three-dimensional terahertz imaging by frequency modulation of a quantum cascade laser in a compact and experimentally simple self-mixing scheme. Through this approach, we can realize significantly faster acquisition rates compared to previous schemes employing longitudinal mechanical scanning of a sample. We achieve a depth resolution of better than 0.1 μm with a power noise spectral density below -50 dB/Hz, for a sampling time of 10 ms/pixel.
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17
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Dean P, Keeley J, Valavanis A, Bertling K, Lim YL, Taimre T, Alhathlool R, Li LH, Indjin D, Rakić AD, Linfield EH, Davies AG. Active phase-nulling of the self-mixing phase in a terahertz frequency quantum cascade laser. Opt Lett 2015; 40:950-953. [PMID: 25768154 DOI: 10.1364/ol.40.000950] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
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.
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18
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Houver S, Cavalié P, St-Jean MR, Amanti MI, Sirtori C, Li LH, Davies AG, Linfield EH, Pereira TAS, Lebreton A, Tignon J, Dhillon SS. Optical sideband generation up to room temperature with mid-infrared quantum cascade lasers. Opt Express 2015; 23:4012-4020. [PMID: 25836440 DOI: 10.1364/oe.23.004012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Mid-infrared (MIR) sideband generation on a near infrared (NIR) optical carrier is demonstrated within a quantum cascade laser (QCL). By employing an externally injected NIR beam, E(NIR), that is resonant with the interband transitions of the quantum wells in the QCL, the nonlinear susceptibility is enhanced, leading to both frequency mixing and sideband generation. A GaAs-based MIR QCL (E(QCL) = 135 meV) with an aluminum-reinforced waveguide was utilized to overlap the NIR and MIR modes with the optical nonlinearity of the active region. The resulting difference sideband (E(NIR) - E(QCL)) shows a resonant behavior as a function of NIR pump wavelength and a maximum second order nonlinear susceptibility, χ((2)), of ~1 nm/V was obtained. Further, the sideband intensity showed little dependence with the operating temperature of the QCL, allowing sideband generation to be realized at room temperature.
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19
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Li LH, Zhu JX, Chen L, Davies AG, Linfield EH. The MBE growth and optimization of high performance terahertz frequency quantum cascade lasers. Opt Express 2015; 23:2720-2729. [PMID: 25836134 DOI: 10.1364/oe.23.002720] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The technique of molecular beam epitaxy has recently been used to demonstrate the growth of terahertz frequency GaAs/AlGaAs quantum cascade lasers (QCL) with Watt-level optical output powers. In this paper, we discuss the critical importance of achieving accurate layer thicknesses and alloy compositions during growth, and demonstrate that precise growth control as well as run-to-run growth reproducibility is possible. We also discuss the importance of minimizing background doping level in maximizing QCL performance. By selecting high-performance active region designs, and optimizing the injection doping level and device fabrication, we demonstrate total optical (two-facet) output powers as high as 1.56 W.
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20
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Dodoo-Amoo NA, Saeed K, Mistry D, Khanna SP, Li L, Linfield EH, Davies AG, Cunningham JE. Non-universality of scaling exponents in quantum Hall transitions. J Phys Condens Matter 2014; 26:475801. [PMID: 25351842 DOI: 10.1088/0953-8984/26/47/475801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We have investigated experimentally the scaling behaviour of quantum Hall transitions in GaAs/AlGaAs heterostructures of a range of mobility, carrier concentration, and spacer layer width. All three critical scaling exponents γ, κ and p were determined independently for each sample. We measure the localization length exponent to be γ ≈ 2.3, in good agreement with expected predictions from scaling theory, but κ and p are found to possess non-universal values. Results obtained for κ range from κ = 0.16 ± 0.02 to κ = 0.67 ± 0.02, and are found to be Landau level (LL) dependent, whereas p is found to decrease with increasing sample mobility. Our results demonstrate the existence of two transport regimes in the LL conductivity peak; universality is found within the quantum coherent transport regime present in the tails of the conductivity peak, but is absent within the classical transport regime found close to the critical point at the centre of the conductivity peak. We explain these results using a percolation model and show that the critical scaling exponent depends on certain important length scales that correspond to the microscopic description of electron transport in the bulk of a two-dimensional electron system.
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Affiliation(s)
- N A Dodoo-Amoo
- School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT,UK
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21
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Halioua Y, Xu G, Moumdji S, Li LH, Davies AG, Linfield EH, Colombelli R. THz quantum cascade lasers operating on the radiative modes of a 2D photonic crystal. Opt Lett 2014; 39:3962-3965. [PMID: 24978782 DOI: 10.1364/ol.39.003962] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Photonic-crystal lasers operating on Γ-point band-edge states of a photonic structure naturally exploit the so-called "nonradiative" modes. As the surface output coupling efficiency of these modes is low, they have relatively high Q factors, which favor lasing. We propose a new 2D photonic-crystal design that is capable of reversing this mode competition and achieving lasing on the radiative modes instead. Previously, this has only been shown in 1D structures, where the central idea is to introduce anisotropy into the system, both at unit-cell and resonator scales. By applying this concept to 2D photonic-crystal patterned terahertz frequency quantum cascade lasers, surface-emitting devices with diffraction-limited beams are demonstrated, with 17 mW peak output power.
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22
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Lui HS, Taimre T, Bertling K, Lim YL, Dean P, Khanna SP, Lachab M, Valavanis A, Indjin D, Linfield EH, Davies AG, Rakić AD. Terahertz inverse synthetic aperture radar imaging using self-mixing interferometry with a quantum cascade laser. Opt Lett 2014; 39:2629-2632. [PMID: 24784063 DOI: 10.1364/ol.39.002629] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We propose a terahertz (THz)-frequency synthetic aperture radar imaging technique based on self-mixing (SM) interferometry, using a quantum cascade laser. A signal processing method is employed which extracts and exploits the radar-related information contained in the SM signals, enabling the creation of THz images with improved spatial resolution. We demonstrate this by imaging a standard resolution test target, achieving resolution beyond the diffraction limit.
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23
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Wood CD, Mistry D, Li LH, Cunningham JE, Linfield EH, Davies AG. On-chip terahertz spectroscopic techniques for measuring mesoscopic quantum systems. Rev Sci Instrum 2013; 84:085101. [PMID: 24007101 DOI: 10.1063/1.4816736] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We present the self-aligned fabrication of on-chip devices in which waveguides, incorporating integrated photoconductive switches, are combined with two-dimensional electron systems to allow probing of the ultrafast (terahertz frequency range) properties of confined semiconductor systems, both at cryogenic temperatures and in high magnetic fields. We demonstrate the direct injection of on-chip terahertz pulses into the mesoscopic system by femtosecond, near infra-red laser excitation of in-plane photoconductive switches formed on an epitaxially grown, low-temperature GaAs layer, which is integrated monolithically with a GaAs∕AlGaAs heterostructure containing a two-dimensional electron system. Both the input and output terahertz signals of an on-chip waveguide are sampled by altering dynamically the photoconductive excitation∕detection arrangement in situ on a single device. We also demonstrate a new method for sub-Kelvin excitation and detection of on-chip terahertz frequency radiation in a (3)He∕(4)He dilution refrigerator that allows the photocurrent and detected terahertz transient to be mapped as function of the near-infrared excitation position at the emitter and the detector, respectively. Furthermore, we demonstrate transmission of terahertz transients through a two-dimensional electron system in a coplanar waveguide under magnetic field at temperatures as low as 200 mK.
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Affiliation(s)
- C D Wood
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
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24
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Abstract
We report the use ofterahertz time-domain spectroscopy for thestudy of two therapeutic bio-molecules:glucose and uric acid. Terahertztransmission spectra of crystalline samplesof both molecules were measured between 0.1-3.0 THz using an evacuated spectroscopysystem. We propose that the stereo-isomersof glucose show spectral featuresoriginating from intermolecular vibrationalmodes, as do uric acid and its derivativemolecule, allantoin. In addition, wepresent a full temperature dependence ofthe terahertz absorption of L-glucose.
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Affiliation(s)
- P C Upadhya
- Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE UK
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25
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Abstract
Visible/near-infraredlaser-induced difference spectroscopy basedon a time-domain terahertz system has beendeveloped, and used to study copperpathancyonine. We find that the absorptionpeak of this molecule at 1.08 THz changessignificantly under 790 nm laserexcitation, suggesting that we haveobserved the first evidence of vibrationalmode changes in the THz range induced byvisible/near-infrared light.
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Affiliation(s)
- Y C Shen
- Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE UK
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Abstract
Terahertz Pulsed Imaging(TPI) is a new medical imaging modality forthe detection of epithelial cancers. Overthe last two years this technique has beenapplied to the study of in vitrobasal cell carcinoma (BCC). Usingtime-domain analysis the contrast betweendiseased and normal tissue has been shownto be statistically significant, andregions of increased terahertz (THz)absorption correlated well with thelocation of the tumour sites in histology.Understanding the source of this contrastthrough frequency-domain analysis mayfacilitate the diagnosis of skin cancer andrelated skin conditions using TPI. Wepresent the first frequency-domain analysisof basal cell carcinoma in vitro,with the raw power spectrum giving aninsight into the surface features of theskin. Further data manipulation is requiredto determine whether spectral informationcan be extrapolated at depth. These resultshighlight the complexity of working inreflection geometry.
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Affiliation(s)
- R M Woodward
- TeraView Limited, 302/304 Science Park, Milton Road, Cambridge, CB4 OWG UK ; Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 OHE UK
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Shen YC, Davies AG, Linfield EH, Taday PF, Arnone DD, Elsey TS. Determination of Glucose Concentration in Whole Blood using Fourier-Transform Infrared Spectroscopy. J Biol Phys 2013; 29:129-33. [PMID: 23345828 DOI: 10.1023/a:1024480423056] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Fourier-transform infrared(FTIR) transmission spectroscopy has beenused for the determination of glucoseconcentrations in whole blood samples fromtwenty-eight patients. A four-vectorpartial least squares calibration model,using the spectral range 950-1200 cm(-1),yielded a standard error of prediction of0.59 mM for an independent test set. Forblood samples from a single patient, wefound that the glucose concentration wasproportional to the difference between thevalues of the second derivative spectrum at1082 cm(-1) and 1093 cm(-1), suggestingthat these two specific wavelengths can beused for determining glucose concentrationsin blood.
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Affiliation(s)
- Y C Shen
- Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE UK
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28
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Maysonnave J, Maussang K, Freeman JR, Jukam N, Madéo J, Cavalié P, Rungsawang R, Khanna SP, Linfield EH, Davies AG, Beere HE, Ritchie DA, Dhillon SS, Tignon J. Mode-locking of a terahertz laser by direct phase synchronization. Opt Express 2012; 20:20855-20862. [PMID: 23037209 DOI: 10.1364/oe.20.020855] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
A novel scheme to achieve mode-locking of a multimode laser is demonstrated. Traditional methods to produce ultrashort laser pulses are based on modulating the cavity gain or losses at the cavity roundtrip frequency, favoring the pulsed emission. Here, we rather directly act on the phases of the modes, resulting in constructive interference for the appropriated phase relationship. This was performed on a terahertz quantum cascade laser by multimode injection seeding with an external terahertz pulse, resulting in phase mode-locked terahertz laser pulses of 9 ps duration, characterized unambiguously in the time domain.
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Affiliation(s)
- J Maysonnave
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université P. et M. Curie, Université D. Diderot, 75231 Paris Cedex 05, France
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29
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Maysonnave J, Jukam N, Ibrahim MSM, Maussang K, Madéo J, Cavalié P, Dean P, Khanna SP, Steenson DP, Linfield EH, Davies AG, Tignon J, Dhillon SS. Integrated injection seeded terahertz source and amplifier for time-domain spectroscopy. Opt Lett 2012; 37:731-733. [PMID: 22344163 DOI: 10.1364/ol.37.000731] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We used a terahertz (THz) quantum cascade laser (QCL) as an integrated injection seeded source and amplifier for THz time-domain spectroscopy. A THz input pulse is generated inside a QCL by illuminating the laser facet with a near-IR pulse from a femtosecond laser and amplified using gain switching. The THz output from the QCL is found to saturate upon increasing the amplitude of the THz input power, which indicates that the QCL is operating in an injection seeded regime.
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Affiliation(s)
- J Maysonnave
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université Pierre et Marie Curie, Université D. Diderot, Paris, France
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30
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Ravaro M, Manquest C, Sirtori C, Barbieri S, Santarelli G, Blary K, Lampin JF, Khanna SP, Linfield EH. Phase-locking of a 2.5 THz quantum cascade laser to a frequency comb using a GaAs photomixer. Opt Lett 2011; 36:3969-3971. [PMID: 22002355 DOI: 10.1364/ol.36.003969] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We report the heterodyne detection and phase locking of a 2.5 THz quantum cascade laser (QCL) using a terahertz frequency comb generated in a GaAs photomixer using a femtosecond fiber laser. With 10 mW emitted by the QCL, the phase-locked signal at the intermediate frequency yields 80 dB of signal-to-noise ratio in a bandwidth of 1 Hz.
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Affiliation(s)
- M Ravaro
- Laboratoire Matériaux et Phénomènes Quantiques, Université Paris Diderot and CNRS (UMR 7162), Paris, France. marco.ravaro@univ‐paris‐diderot.fr
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31
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Dean P, Burnett AD, Tych K, Khanna SP, Lachab M, Cunningham JE, Linfield EH, Davies AG. Measurement and analysis of the diffuse reflectance of powdered samples at terahertz frequencies using a quantum cascade laser. J Chem Phys 2011; 134:134304. [DOI: 10.1063/1.3575201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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32
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Lever L, Hinchcliffe NM, Khanna SP, Dean P, Ikonic Z, Evans CA, Davies AG, Harrison P, Linfield EH, Kelsall RW. Terahertz ambipolar dual-wavelength quantum cascade laser. Opt Express 2009; 17:19926-19932. [PMID: 19997216 DOI: 10.1364/oe.17.019926] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Terahertz frequency quantum cascade lasers (THz QCLs) are compact solid-state sources of terahertz radiation that were first demonstrated in 2002. They have a broad range of potential applications ranging from gas sensing and non-destructive testing, through to security and medical imaging, with many polycrystalline compounds having distinct fingerprint spectra in the terahertz frequency range. In this article, we demonstrate an electrically-switchable dual-wavelength THz QCL which will enable spectroscopic information to be obtained within a THz QCL-based imaging system. The device uses the same active region for both emission wavelengths: in forward bias, the laser emits at 2.3 THz; in reverse bias, it emits at 4 THz. The corresponding threshold current densities are 490 A/cm(2) and 330 A/cm(2), respectively, with maximum operating temperatures of 98K and 120 K.
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Affiliation(s)
- L Lever
- Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom.
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Chassagneux Y, Colombelli R, Maineults W, Barbieri S, Khanna SP, Linfield EH, Davies AG. Predictable surface emission patterns in terahertz photonic-crystal quantum cascade lasers. Opt Express 2009; 17:9491-9502. [PMID: 19506596 DOI: 10.1364/oe.17.009491] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We demonstrate a framework to understand and predict the far-field emission in terahertz frequency photonic-crystal quantum cascade lasers. The devices, which employ a high-performance three-well active region, are lithographically tunable and emit in the 104-120 microm wavelength range. A peak output power of 7 mW in pulsed mode is obtained at 10 K, and the typical device maximum operating temperature is 136 K. We identify the photonic-crystal band-edge states involved in the lasing process as originating from the hexapole and monopole modes at the G point of the photonic band structure, as designed. The theoretical far-field patterns, obtained via finite-difference time-domain simulations, are in excellent agreement with experiment. Polarization measurements further support the theory, and the role of the bonding wires in the emission process is elucidated.
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Affiliation(s)
- Y Chassagneux
- Institut d'Electronique Fondamentale, Université Paris-Sud and CNRS, UMR8622, Orsay, France.
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34
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Shaukat MU, Dean P, Khanna SP, Lachab M, Chakraborty S, Linfield EH, Davies AG. Generation of Bessel beams using a terahertz quantum cascade laser. Opt Lett 2009; 34:1030-1032. [PMID: 19340209 DOI: 10.1364/ol.34.001030] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We report the generation of Bessel beams using polytetrafluoroethene conical lenses and a quantum cascade laser emitting at 2.8 THz. The formation of a central beam spot that retains its size over distances exceeding the characteristic Rayleigh range is demonstrated, and the power transport properties of these beams are compared with those obtained using parabolic reflectors. These lenses could provide an attractive alternative to parabolic reflectors for terahertz imaging applications where a large depth of focus and/or efficient and controllable coupling of radiation onto a small target are desirable.
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Affiliation(s)
- M U Shaukat
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, UK
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35
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Fan WH, Burnett A, Upadhya PC, Cunningham J, Linfield EH, Davies AG. Far-infrared spectroscopic characterization of explosives for security applications using broadband terahertz time-domain spectroscopy. Appl Spectrosc 2007; 61:638-43. [PMID: 17650376 DOI: 10.1366/000370207781269701] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Broadband terahertz time-domain spectroscopy (THz-TDS) has been used to measure the far-infrared (FIR) vibrational spectra of several commonly used pure explosives, including 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), 1,3-dinitrato-2,2-bis(nitratomethyl)propane (PETN), and two types of plastic explosive, SEMTEX and SX2. A number of distinct absorption peaks, originating from FIR-active vibrational modes of these polycrystalline energetic materials, were observed in the frequency range 0.3-7.5 THz (10-250 cm(-1)). In addition, the temperature-dependent FIR vibrational spectra of PETN were measured between 4 K and 296 K with several well-resolved absorption peaks observed across this temperature range. We find that as the temperature is reduced, the observed absorption peaks resolve into narrower features and shift towards higher frequencies. The temperature dependence of the spectra is explained in terms of the anharmonicity of the vibrational potentials of crystalline compounds, and an empirical fit is given to describe the peak shift with temperature.
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Affiliation(s)
- W H Fan
- School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom.
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36
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37
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Barbieri S, Alton J, Beere HE, Linfield EH, Ritchie DA, Withington S, Scalari G, Ajili L, Faist J. Heterodyne mixing of two far-infrared quantum cascade lasers by use of a point-contact Schottky diode. Opt Lett 2004; 29:1632-1634. [PMID: 15309842 DOI: 10.1364/ol.29.001632] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We demonstrate heterodyne mixing of two free-running, multimode, 3.3-THz quantum cascade lasers by use of a point-contact Schottky diode. By temperature tuning the emission wavelength of one laser, a difference frequency signal spanning the 2-4-GHz range is obtained, with a signal-to-noise ratio of 30 dB. The frequency of the heterodyne signal is subject to random fluctuations of a few megahertz, principally from instabilities in the temperatures of the devices. From single-shot measurements we derive an instantaneous linewidth for a single Fabry-Perot mode of 20 kHz, corresponding to an integration time of 3.6 ms.
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Affiliation(s)
- S Barbieri
- TeraView, Ltd., Science Park, Cambridge, UK.
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38
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Giazotto F, Grove-Rasmussen K, Fazio R, Beltram F, Linfield EH, Ritchie DA. Josephson Current in Nb/InAs/Nb Highly Transmissive Ballistic Junctions. ACTA ACUST UNITED AC 2004. [DOI: 10.1023/b:josc.0000021231.01260.94] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Barkan A, Tittel FK, Mittleman DM, Dengler R, Siegel PH, Scalari G, Ajili L, Faist J, Beere HE, Linfield EH, Davies AG, Ritchie DA. Linewidth and tuning characteristics of terahertz quantum cascade lasers. Opt Lett 2004; 29:575-577. [PMID: 15035475 DOI: 10.1364/ol.29.000575] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We have measured the spectral linewidths of three continuous-wave quantum cascade lasers operating at terahertz frequencies by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers. Beat notes are detected with a GaAs diode mixer and a microwave spectrum analyzer, permitting very precise frequency measurements and giving instantaneous linewidths of less than -30 kHz. Characteristics are also reported for frequency tuning as the injection current is varied.
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Affiliation(s)
- A Barkan
- Department of Electrical and Computer Engineering, MS-366, Rice University, Houston, Texas 77251-1892, USA
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40
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Safonov SS, Savchenko AK, Bagrets DA, Jouravlev ON, Nazarov YV, Linfield EH, Ritchie DA. Enhanced shot noise in resonant tunneling via interacting localized states. Phys Rev Lett 2003; 91:136801. [PMID: 14525327 DOI: 10.1103/physrevlett.91.136801] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2003] [Indexed: 05/24/2023]
Abstract
In a variety of mesoscopic systems shot noise is seen to be suppressed in comparison with its Poisson value. In this work we observe a considerable enhancement of shot noise in the case of resonant tunneling via localized states. We present a model of correlated transport through two localized states which provides both a qualitative and a quantitative description of this effect.
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Affiliation(s)
- S S Safonov
- School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, United Kingdom
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41
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Li L, Proskuryakov YY, Savchenko AK, Linfield EH, Ritchie DA. Magnetoresistance of a 2D electron gas caused by electron interactions in the transition from the diffusive to the ballistic regime. Phys Rev Lett 2003; 90:076802. [PMID: 12633258 DOI: 10.1103/physrevlett.90.076802] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2002] [Indexed: 05/24/2023]
Abstract
On a high-mobility 2D electron gas we have observed, in strong magnetic fields (omega(c)tau>1), a parabolic negative magnetoresistance caused by electron-electron interactions in the regime of k(B)Ttau/ variant Planck's over 2pi approximately 1, which is the transition from the diffusive to the ballistic regime. From the temperature dependence of this magnetoresistance the interaction correction to the conductivity deltasigma(ee)(xx)(T) is obtained in the situation of a long-range fluctuation potential and strong magnetic field. The results are compared with predictions of the new theory of interaction-induced magnetoresistance.
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Affiliation(s)
- L Li
- School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, United Kingdom
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42
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Abstract
The terahertz region of the electromagnetic spectrum spans the frequency range between the mid-infrared and the millimetre/microwave. This region has not been exploited fully to date owing to the limited number of suitable (in particular, coherent) radiation sources and detectors. Recent demonstrations, using pulsed near-infrared femtosecond laser systems, of the viability of THz medical imaging and spectroscopy have sparked international interest; yet much research still needs to be undertaken to optimize both the power and bandwidth in such THz systems. In this paper, we review how femtosecond near-infrared laser pulses can be converted into broad band THz radiation using semiconductor crystals, and discuss in depth the optimization of one specific generation mechanism based on ultra-fast transport of electrons and holes at a semiconductor surface. We also outline a few of the opportunities for a technology that can address a diverse range of challenges spanning the physical and biological sciences, and note the continuing need for the development of solid state, continuous wave, THz sources which operate at room temperature.
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Affiliation(s)
- A G Davies
- Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK.
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43
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Johnston MB, Whittaker DM, Dowd A, Davies AG, Linfield EH, Li X, Ritchie DA. Generation of high-power terahertz pulses in a prism. Opt Lett 2002; 27:1935-1937. [PMID: 18033407 DOI: 10.1364/ol.27.001935] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A compact, high-power emitter of half-cycle terahertz (THz) radiation is demonstrated. The device consists of an epitaxial InAs emitter upon a GaAs prism and produces THz pulses that are 20 times more powerful than those from conventional planar InAs emitters. This improvement is a direct result of reorienting the transient THz dipole such that its axis is not perpendicular to the emitting surface.
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44
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Zolleis KR, Ford CJB, Kardynal B, Ritchie DA, Linfield EH, Rose PD, Jones GAC. Tunneling spectroscopy of a two-dimensionally periodic electron system. Phys Rev Lett 2002; 89:146803. [PMID: 12366065 DOI: 10.1103/physrevlett.89.146803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2001] [Indexed: 05/23/2023]
Abstract
The tunneling current between an electron gas with a periodic potential in two dimensions and a plain two-dimensional electron system (2DES) has been studied. The strength of the periodic potential, the subband energy of the plain 2DES, and an applied in-plane magnetic field were varied, mapping the Fourier transform of the periodic wave function. Periodic peaks were observed and explained by translations in the reciprocal lattice. When the potential was strongly modulated to form an array of antidots, commensurability peaks were seen in lateral transport, but, as expected, not in tunneling.
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Affiliation(s)
- K R Zolleis
- Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, United Kingdom
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45
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Hamilton AR, Simmons MY, Pepper M, Linfield EH, Ritchie DA. Metallic behavior in dilute two-dimensional hole systems. Phys Rev Lett 2001; 87:126802. [PMID: 11580536 DOI: 10.1103/physrevlett.87.126802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2000] [Indexed: 05/23/2023]
Abstract
We have studied the metallic behavior in low-density two-dimensional p-GaAs systems, close to the apparent metal-insulator transition. Two observations are made concerning the origins of the metallic-like behavior. Within a given sample the strength of the metallic behavior is almost independent of the asymmetry of the confining potential, and is predominantly determined by the low-temperature resistivity (i.e., by k(F)l). In all our samples we find that at low densities, close to the transition from insulating to metallic behavior, the fractional decrease in conductivity with increasing temperature scales as T/T(F).
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Affiliation(s)
- A R Hamilton
- School of Physics, The University of New South Wales, Sydney 2052, Australia
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46
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Micolich AP, Taylor RP, Davies AG, Bird JP, Newbury R, Fromhold TM, Ehlert A, Linke H, Macks LD, Tribe WR, Linfield EH, Ritchie DA, Cooper J, Aoyagi Y, Wilkinson PB. Evolution of fractal patterns during a classical-quantum transition. Phys Rev Lett 2001; 87:036802. [PMID: 11461579 DOI: 10.1103/physrevlett.87.036802] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2000] [Indexed: 05/23/2023]
Abstract
We investigate how fractals evolve into nonfractal behavior as the generation process is gradually suppressed. Fractals observed in the conductance of semiconductor billiards are of particular interest because the generation process is semiclassical and can be suppressed by transitions towards either fully classical or fully quantum-mechanical conduction. Investigating a range of billiards, we identify a "universal" behavior in the changeover from fractal to nonfractal conductance, which is described by a smooth evolution rather than deterioration in the fractal scaling properties.
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Affiliation(s)
- A P Micolich
- Materials Science Institute, Physics Department, University of Oregon, Eugene, Oregon 97403-1274, USA
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47
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Simmons MY, Hamilton AR, Pepper M, Linfield EH, Rose PD, Ritchie DA. Weak localization, hole-hole interactions, and the "Metal"-insulator transition in two dimensions. Phys Rev Lett 2000; 84:2489-2492. [PMID: 11018917 DOI: 10.1103/physrevlett.84.2489] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/1999] [Indexed: 05/23/2023]
Abstract
A detailed investigation of the metallic behavior in high-quality GaAs-AlGaAs two-dimensional hole systems reveals the presence of quantum corrections to the resistivity at low temperatures. Despite the low density ( r(s)>10) and high quality of these systems, both weak localization (observed via negative magnetoresistance) and weak hole-hole interactions (giving a correction to the Hall constant) are present in the so-called metallic phase where the resistivity decreases with decreasing temperature. If these quantum corrections persist down to T = 0, the results suggest that even at high r(s) there is no metallic phase in two dimensions.
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Affiliation(s)
- MY Simmons
- Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 OHE, United Kingdom and Semiconductor Nanofabrication Facility, University of New South Wales, Sydney 2052, Australia
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48
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Shapira S, Linfield EH, Lambert CJ, Seviour R, Volkov AF, Zaitsev AV. Anomalous behavior of superconducting-normal mesoscopic structures near T(c). Phys Rev Lett 2000; 84:159-162. [PMID: 11015859 DOI: 10.1103/physrevlett.84.159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/1999] [Indexed: 05/23/2023]
Abstract
We observe a maximum in the conductance of Al/n-GaAs junctions at temperatures 20 mK lower than the superconducting transition temperature (T(c)). This is the first observation of a peak in the conductance near the superconducting transition in superconducting-normal (S/N) junctions. To accommodate this effect we calculate the full temperature dependence of the conductance of these structures, invoking quasiclassical Green's functions in the diffusive limit. In addition to the well-known low-temperature peak at temperatures on the order of the Thouless energy, we find a maximum near T(c). This peak has the same origin as the subgap conductance observed in S/N junctions at low temperatures.
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Affiliation(s)
- S Shapira
- Cavendish Laboratory, University of Cambridge, Madingley Road CB3 0HE, United Kingdom
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49
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Turner N, Nicholls JT, Linfield EH, Brown KM, Jones GA, Ritchie DA. Tunneling between parallel two-dimensional electron gases. Phys Rev B Condens Matter 1996; 54:10614-10624. [PMID: 9984858 DOI: 10.1103/physrevb.54.10614] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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50
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Hughes RJ, Savchenko AK, Frost JE, Linfield EH, Nicholls JT, Pepper M, Kogan E, Kaveh M. Distribution-function analysis of mesoscopic hopping conductance fluctuations. Phys Rev B Condens Matter 1996; 54:2091-2100. [PMID: 9986060 DOI: 10.1103/physrevb.54.2091] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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