Abstract-Investigation of hollow cylindrical metal terahertz waveguides suitable for cryogenic environments

R. Wallis, R. Degl Innocenti, D. S. Jessop, O. Mitrofanov, C. M. Bledt, J. E. Melzer, J. A. Harrington, H. E. Beere, and D. A. Ritchie

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-26-30002

The field of terahertz (THz) waveguides continues to grow rapidly, with many being tailored to suit the specific demands of a particular final application. Here, we explore waveguides capable of enabling efficient and accurate power delivery within cryogenic environments (< 4 K). The performance of extruded hollow cylindrical metal waveguides made of un-annealed and annealed copper, as well as stainless steel, have been investigated for bore diameters between 1.75 - 4.6 mm, and at frequencies of 2.0, 2.85 and 3.4 THz, provided by a suitable selection of THz quantum cascade lasers. The annealed copper resulted in the lowest transmission losses, < 3 dB/m for a 4.6 mm diameter waveguide, along with 90° bending losses as low as ~2 dB for a bend radius of 15.9 mm. The observed trends in losses were subsequently analyzed and related to measured inner surface roughness parameters. These results provide a foundation for the development of a wide array of demanding low-temperature THz applications, and enabling the study of fundamental physics.

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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Abstract-Monte Carlo simulation of near-field terahertz emission from semiconductors

S. C. Corzo-Garcia, A. I. Hernandez-Serrano, E. Castro-Camus, and O. Mitrofanov

Phys. Rev. B 94, 045301 – Published 1 July 2016

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.045301

We simulated the carrier dynamics in InGaAs after ultrafast photoexcitation. By using a finite-difference time-domain approach we were able to analyze the near terahertz field emission caused by the motion of such carriers. We found that both the current parallel and normal to the interface take a relevant role in the terahertz emission. We also found that the ballistic motion of the carriers after photoexcitation dominates the emission rather than diffusion.

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Abstract-Efficient coupling of double-metal terahertz quantum cascade lasers to flexible dielectric-lined hollow metallic waveguides

R. Wallis, R. Degl’Iinnocenti, D. S. Jessop, Y. Ren, A. Klimont, Y. D. Shah, O. Mitrofanov, C. M. Bledt, J. E. Melzer, J. A. Harrington, H. E. Beere, and D. A. Ritchie
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-20-26276

The growth in terahertz frequency applications utilising the quantum cascade laser is hampered by a lack of targeted power delivery solutions over large distances (>100 mm). Here we demonstrate the efficient coupling of double-metal quantum cascade lasers into flexible polystyrene lined hollow metallic waveguides via the use of a hollow copper waveguide integrated into the laser mounting block. Our approach exhibits low divergence, Gaussian-like emission, which is robust to misalignment error, at distances > 550 mm, with a coupling efficiency from the hollow copper waveguide into the flexible waveguide > 90%. We also demonstrate the ability to nitrogen purge the flexible waveguide, increasing the power transmission by up to 20% at 2.85 THz, which paves the way for future fibre based terahertz sensing and spectroscopy applications.

© 2015 Optical Society of America

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Abstract-Hollow metallic waveguides integrated with terahertz quantum cascade lasers

R. Degl’Innocenti, Y. D. Shah, D. S. Jessop, Y. Ren, O. Mitrofanov, H. E. Beere, and D. A. Ritchie  »View Author Affiliations

Optics Express, Vol. 22, Issue 20, pp. 24439-24449 (2014)
http://dx.doi.org/10.1364/OE.22.024439

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-20-24439

We present the realization of a compact, monolithically integrated arrangement of terahertz quantum cascade lasers with hollow metallic cylindrical waveguides. By directly mounting a copper pipe to the end facet of a double metal waveguide, it was possible to significantly improve the far field emission from such a sub-wavelength plasmonic mode, while preserving the characteristic performance of the laser. Careful alignment of the quantum cascade laser and the hollow waveguide is required in order to prevent the excitation of higher order/mixed modes as predicted with a high degree of accuracy by a theoretical model. Finally, this approach proved to be a superior method of beam shaping when compared to other in situarrangements, such as a silicon hyper-hemispherical lens glued to the facet, which are presented.

© 2014 Optical Society of America