Abstract-On-chip Terahertz-Frequency Measurements of Liquids

Matthew Swithenbank, Andrew David Burnett, Christopher Russell, Lianhe H. Li, Alexander Giles Davies, Edmund H. Linfield, John E. Cunningham, and Christopher David Wood

Anal. Chem., Just Accepted Manuscript

DOI: 10.1021/acs.analchem.7b01235

Publication Date (Web): July 6, 2017

Copyright © 2017 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.analchem.7b01235?journalCode=ancham

Terahertz-frequency-range measurements can offer potential insight into the picosecond dynamics, and therefore function, of many chemical systems. There is a need to develop technologies capable of performing such measurements in aqueous and polar environments, particularly when it is necessary to maintain the full functionality of biological samples. In this study, we present a proof-of-concept technology comprising an on-chip planar Goubau line, integrated with a microfluidic channel, which is capable of low-loss, terahertz-frequency-range spectroscopic measurements of liquids. We also introduce a mathematical model that accounts for changes in the electric field distribution around the waveguide, allowing accurate, frequency-dependent liquid parameters to be extracted. We demonstrate the sensitivity of this technique by measuring a homologous alcohol series across the 0.1-0.8 THz frequency range.

Abstract-Quasi-continuous frequency tunable terahertz quantum cascade lasers with coupled cavity and integrated photonic lattice

Iman Kundu, Paul Dean, Alexander Valavanis, Li Chen, Lianhe Li, John E. Cunningham, Edmund H. Linfield, and A. Giles Davies

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-1-486

We demonstrate quasi-continuous tuning of the emission frequency from coupled cavity terahertz frequency quantum cascade lasers. Such coupled cavity lasers comprise a lasing cavity and a tuning cavity which are optically coupled through a narrow air slit and are operated above and below the lasing threshold current, respectively. The emission frequency of these devices is determined by the Vernier resonance of longitudinal modes in the lasing and the tuning cavities, and can be tuned by applying an index perturbation in the tuning cavity. The spectral coverage of the coupled cavity devices have been increased by reducing the repetition frequency of the Vernier resonance and increasing the ratio of the free spectral ranges of the two cavities. A continuous tuning of the coupled cavity modes has been realized through an index perturbation of the lasing cavity itself by using wide electrical heating pulses at the tuning cavity and exploiting thermal conduction through the monolithic substrate. Single mode emission and discrete frequency tuning over a bandwidth of 100 GHz and a quasi-continuous frequency coverage of 7 GHz at 2.25 THz is demonstrated. An improvement in the side mode suppression and a continuous spectral coverage of 3 GHz is achieved without any degradation of output power by integrating a π-phase shifted photonic lattice in the laser cavity.

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Abstract-Time-domain measurement of terahertz frequency magnetoplasmon resonances in a two-dimensional electron system by the direct injection of picosecond pulsed currents

Jingbo Wu1, Oleksiy Sydoruk2, Alexander S. Mayorov1, Christopher D. Wood1, Divyang Mistry1, Lianhe Li1, Edmund H. Linfield1, A. Giles Davies1 and John E. Cunningham1,a)
http://scitation.aip.org/content/aip/journal/apl/108/9/10.1063/1.4943173
1 School of Electronic and Electrical Engineering, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, United Kingdom
2 Optical and Semiconductor Devices Group, Department of Electrical and Electronic Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
a) Electronic email: j.e.cunningham@leeds.ac.uk
Appl. Phys. Lett. 108, 091109 (2016); http://dx.doi.org/10.1063/1.4943173

We have investigated terahertz (THz) frequency magnetoplasmon resonances in a two-dimensional electron system through the direct injection of picosecond duration current pulses. The evolution of the time-domain signals was measured as a function of magnetic field, and the results were found to be in agreement with calculations using a mode-matching approach for four modes observed in the frequency range above 0.1 THz. This introduces a generic technique suitable for sampling ultrafast carrier dynamics in low-dimensional semiconductor nanostructures at THz frequencies.

Abstract-Discrete Vernier tuning in terahertz quantum cascade lasers using coupled cavities

Iman Kundu, Paul Dean, Alexander Valavanis, Li Chen, Lianhe Li, John E. Cunningham, Edmund H. Linfield, and A. Giles Davies  »View Author Affiliations

Optics Express, Vol. 22, Issue 13, pp. 16595-16605 (2014)
http://dx.doi.org/10.1364/OE.22.016595

http://8.18.37.105/oe/abstract.cfm?uri=oe-22-13-16595

Discrete Vernier frequency tuning of terahertz quantum cascade lasers is demonstrated using a device comprising a two-section coupled-cavity. The two sections are separated by a narrow air gap, which is milled after device packaging using a focused ion beam. One section of the device (the lasing section) is electrically biased above threshold using a short current pulse, while the other section (the tuning section) is biased below threshold with a wider current pulse to achieve controlled localized electrical heating. The resulting thermally-induced shift in the longitudinal cavity modes of the tuning section is engineered to produce either a controllable blue shift or red shift of the emission frequency. This discrete Vernier frequency tuning far exceeds the tuning achievable from standard ridge lasers, and does not lead to any corresponding change in emitted power. Discrete tuning was observed over bandwidths of 50 and 85 GHz in a pair of devices, each using different design schemes. Interchanging the lasing and tuning sections of the same devices yielded red shifts of 20 and 30 GHz, respectively.

© 2014 Optical Society of America