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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Optics and Lasers".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 19836

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Special Issue Editors

Dr. Miguel Beruete

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Guest Editor

1. Antennas Group—TERALAB, Department of Electric, Electronic and Communication Engineering, Universidad Pública de Navarra (UPNA), Campus Arrosadia, 31006 Pamplona, Navarra, Spain
2. Institute of Smart Cities (ISC), Universidad Pública de Navarra (UPNA), Campus Arrosadia, 31006 Pamplona, Navarra, Spain
3. Multispectral Biosensing Group, Navarrabiomed, Complejo Hospitalario de Navarra (CHN), Universidad Pública de Navarra (UPNA), IdiSNA. Irunlarrea 3, 31008 Pamplona, Navarra, Spain
Interests: quasi-optical devices in THz and infrared frequencies, metasurfaces; nanoantennas; antennas based on extraordinary transmission; volumetric metamaterials; with special attention to volumetric devices such as lenses; prisms; beam directors

Prof. Dr. Bakhtiyar Orazbayev

E-Mail Website
Guest Editor

Laboratory of Wave Engineering (LWE), Ecole Polytechnique Fédérale de Lausanne (EPFL), EPFL-Station 11, CH-1015 Lausanne, Switzerland
Interests: metamaterials; metasurfaces; terahertz; antennas; subwavelength imaging.

Dr. Victor Pacheco Peña

E-Mail Website
Guest Editor

School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
Interests: terahertz; antennas; lenses; sensors; metamaterials; metasurfaces; 2D materials; imaging systems; wave–matter interaction
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Special Issue Information

Dear Colleagues,

Today, the terahertz range is experiencing a remarkable surge of interest thanks to the discovery and development of new sources and detectors that have unveiled this, until recently, elusive frequency range of the electromagnetic spectrum. Terahertz sensing of substances and materials and, more specifically, biosensing is an emerging research field for a variety of reasons: Terahertz waves are non-ionizing, they can penetrate polar materials like paper and plastics, and more importantly, they are sensitive to weak interactions and to water content in the biological substances. Moreover, the terahertz band is the limit between microwaves and infrared and, hence, benefits from the latest developments in either range, such as metamaterials and plasmonics.

In this Special Issue, an up-to-date overview of terahertz sensing applications is pursued. A particular interest is dedicated to new sensing platforms based on metamaterials and plasmonics, but also other aspects of biosensing are covered. All this together will help to get a general taste of the latest advances in this emerging and exciting topic.

Prof. Dr. Miguel Beruete
Prof. Dr. Bakhtiyar Orazbayev
Prof. Dr. Victor Pacheco Peña
Guest Editors

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Keywords

Terahertz
Sensors
Biosensors
Metamaterials
Metasurfaces
Spectroscopy

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Published Papers (6 papers)

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Research

18 pages, 4971 KiB

Open AccessArticle

Experimental Measurement of Sharp THz Absorption Signatures from Nucleic Acid Solutions in Nanofluidic Channels

by Elliott R. Brown and Edgar A. Mendoza

Appl. Sci. 2021, 11(24), 11827; https://doi.org/10.3390/app112411827 - 13 Dec 2021

Viewed by 2204

Abstract

We report on the room-temperature experimental measurement of THz absorption signatures in aqueous, double-stranded nucleic acid solutions confined to the submicron silica channels on fused quartz substrates using THz frequency-domain (photomixing) spectroscopy. Three sharp (i.e., strong and narrow) signatures, ~10–20 GHz FWHM, are observed in the shortest base pair sample—small interfering, double-stranded (ds) RNA—in the range of 800 GHz to 1.1 THz. Three similar signatures are also observed in a 50-bp dsDNA ladder sample. For a 1-kbp dsDNA ladder sample, the three are still evident, but are broadened and weakened. For a 48.5-kbp sample (λ-DNA), no prominent signatures are observed, but rather a quasi-sinusoidal transmittance spectrum consistent with a substrate etalon effect. The division between sharp signatures and no signatures is consistent with the molecular length being shorter or longer than the persistence length. Full article

(This article belongs to the Special Issue Terahertz Sensing)

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16 pages, 6604 KiB

Open AccessArticle

“Perfect” Terahertz Vortex Beams Formed Using Diffractive Axicons and Prospects for Excitation of Vortex Surface Plasmon Polaritons

by Boris Knyazev, Valery Cherkassky and Oleg Kameshkov

Appl. Sci. 2021, 11(2), 717; https://doi.org/10.3390/app11020717 - 13 Jan 2021

Cited by 12 | Viewed by 3389

Abstract

Transformation of a Bessel beam by a lens results in the formation of a “perfect” vortex beam (PVB) in the focal plane of the lens. The PVB has a single-ring cross-section and carries an orbital angular momentum (OAM) equal to the OAM of the “parent” beam. PVBs have numerous applications based on the assumption of their ideal ring-type structure. For instance, we proposed using terahertz PVBs to excite vortex surface plasmon polaritons propagating along cylindrical conductors and the creation of plasmon multiplex communication lines in the future (Comput. Opt. 2019, 43, 992). Recently, we demonstrated the formation of PVBs in the terahertz range using a Bessel beam produced using a spiral binary silicon axicon (Phys. Rev. A 2017, 96, 023846). It was shown that, in that case, the PVB was not annular, but was split into nested spiral segments, which was obviously a consequence of the method of Bessel beam generation. The search for methods of producing perfect beams with characteristics approaching theoretically possible ones is a topical task. Since for the terahertz range, there are no devices like spatial modulators of light in the visible range, the main method for controlling the mode composition of beams is the use of diffractive optical elements. In this work, we investigated the characteristics of perfect beams, the parent beams being quasi-Bessel beams created by three types of diffractive phase axicons made of high-resistivity silicon: binary, kinoform, and “holographic”. The amplitude-phase distributions of the field in real perfect beams were calculated numerically in the approximation of the scalar diffraction theory. An analytical expression was obtained for the case of the binary axicon. It was shown that a distribution closest to an ideal vortex was obtained using a holographic axicon. The resulting distributions were compared with experimental and theoretical distributions of the evanescent field of a plasmon near the gold–zinc sulfide–air surface at different thicknesses of the dielectric layer, and recommendations for experiments were given. Full article

(This article belongs to the Special Issue Terahertz Sensing)

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9 pages, 2090 KiB

Open AccessArticle

Tripod-Loop Metasurfaces for Terahertz-Sensing Applications: A Comparison

by Irati Jáuregui-López, Bakhtiyar Orazbayev, Victor Pacheco-Peña and Miguel Beruete

Appl. Sci. 2020, 10(18), 6504; https://doi.org/10.3390/app10186504 - 18 Sep 2020

Cited by 5 | Viewed by 2575

Abstract

The high electric field intensity achieved on the surface of sensors based on metasurfaces (metasensors) makes them an excellent alternative for sensing applications where the volume of the sample to be identified is tiny (for instance, thin-film sensing devices). Various shapes and geometries have been proposed recently for the design of these metasensors unit-cells (meta-atoms) such as split ring resonators or hole arrays, among others. In this paper, we propose, design, and evaluate two types of tripod metasurfaces with different complexity in their geometry. An in-depth comparison of their performance is presented when using them as thin-film sensor devices. The meta-atoms of the proposed metasensors consist of a simple tripod and a hollow tripod structure. From numerical calculations, it is shown that the best geometry to perform thin-film sensing is the compact hollow tripod (due to the highest electric field on its surface) with a mean sensitivity of 3.72 × 10⁻⁵ nm⁻¹. Different modifications are made to this structure to improve this value, such as introducing arms in the design and rotating the metallic pattern 30 degrees. The best sensitivity achieved for extremely thin film analytes (5–25 nm thick) has an average value of 1.42 × 10⁻⁴ nm, which translates into an extremely high improvement of 381% with respect to the initial hollow tripod structure. Finally, a comparison with other designs found in the literature shows that our design is at the top of the ranking, improving the overall performance by more than one order of magnitude. These results highlight the importance of using metastructures with more complex geometries so that a higher electric field intensity distribution and, therefore, designs with better performance can be obtained. Full article

(This article belongs to the Special Issue Terahertz Sensing)

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12 pages, 5390 KiB

Open AccessFeature PaperArticle

Exploiting Localized Surface Plasmon Resonances in Subwavelength Spiral Disks for THz Thin Film Sensing

by Vasily V. Gerasimov, Ruslan R. Hafizov, Sergei A. Kuznetsov and Pavel A. Lazorskiy

Appl. Sci. 2020, 10(10), 3595; https://doi.org/10.3390/app10103595 - 22 May 2020

Cited by 5 | Viewed by 3284

Abstract

In this paper, we studied the sensing performance of metasurfaces comprised by spiral-disk-shaped metallic elements patterned on polypropylene substrates, which exhibited localized surface plasmon resonances in the low-frequency region of the terahertz (THz) spectrum (0.2–0.5 THz). Optimal designs of spiral disks with C-shaped resonators placed near the disks were determined and fabricated. The experimentally measured transmittance spectra of the samples coated with very thin photoresistive layers (d ~ 10⁻⁴–10⁻³ λ) showed good agreement with the simulations. The resonance frequency shift Δf increases with increasing d, while saturating near d = 50 µm. The narrow-band magnetic dark modes excited on symmetrical spiral disks with a 90° C-resonator demonstrated very high figure of merit (FOM) values reaching 1670 (RIU·mm)⁻¹ at 0.3 μm thick analyte. The hybrid high order resonances excited on asymmetrical densely packed spiral disks showed about two times larger FOM values (up to 2950 (RIU·mm)⁻¹) compared to symmetrical distantly spaced spirals that resembled the best FOM results found in the literature for metasurfaces fabricated with a similar technique. The demonstrated high sensing performance of spiral disks is evaluated to be promising for bio-sensing applications in the THz range. Full article

(This article belongs to the Special Issue Terahertz Sensing)

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12 pages, 1922 KiB

Open AccessArticle

Optical and Galvanomagnetic Properties of Bi_1-xSb_x Thin Films in the Terahertz Frequency Range

by Anton D. Zaitsev, Petr S. Demchenko, Dmitry V. Zykov, Ekaterina A. Korotina, Elena S. Makarova, Ivan L. Tkhorzhevskiy, Anastasiia S. Tukmakova, Natallya S. Kablukova, Aleksei V. Asach, Anna V. Novotelnova and Mikhail K. Khodzitsky

Appl. Sci. 2020, 10(8), 2724; https://doi.org/10.3390/app10082724 - 15 Apr 2020

Cited by 14 | Viewed by 3282

Abstract

We report results of galvanomagnetic and terahertz time-domain spectroscopy measurements on thin films of Bi

_{1 - x}

_{x}

on polyimide and mica substrates with various antimony concentrations (x from 0 to 15 %) and film thickness (70, 150 nm). The [...] Read more.

We report results of galvanomagnetic and terahertz time-domain spectroscopy measurements on thin films of Bi

_{1 - x}

_{x}

on polyimide and mica substrates with various antimony concentrations (x from 0 to 15 %) and film thickness (70, 150 nm). The resistivity, Hall coefficient and magnetoresistivity of the films were measured experimentally in the magnetic field of 0.65 T at room temperature. Mobility and concentration of electrons and holes in the film plane were calculated using the transport coefficients. The terahertz time-domain spectroscopy is used to measure the complex conductivity and permittivity of Bi

_{1 - x}

_{x}

thin films on the dielectric substrates in the frequency range from 0.2 to 1 THz. The plasma frequency, relaxation time, DC conductivity and effective carrier mass were extracted from these data and evaluated as functions of the Sb concentration for different film thickness and substrate. We observed that the film magnetoresistivity decreases with increasing the Sb concentration and for most of the films the Hall coefficient is negative and depends on the external factors insignificantly. We show that the mobility of charge carriers weakly depends on Sb concentration, which confirms the assertion about the scattering of carriers on themselves and not on defects in the structure. It was revealed that film static and dynamic resistivity (conductivity) as well as dielectric permittivity depend on Sb content and the film thickness. The results may be used for development of various thermoelectric, electronic and optical devices, such as THz detectors or components which can control the properties of THz radiation. Full article

(This article belongs to the Special Issue Terahertz Sensing)

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14 pages, 15166 KiB

Open AccessArticle

FEM Simulation of THz Detector Based on Sb and Bi₈₈Sb₁₂ Thermoelectric Thin Films

by Anastasiia S. Tukmakova, Alexei V. Asach, Anna V. Novotelnova, Ivan L. Tkhorzhevskiy, Natallya S. Kablukova, Petr S. Demchenko, Anton D. Zaitsev and Mikhail K. Khodzitsky

Appl. Sci. 2020, 10(6), 1929; https://doi.org/10.3390/app10061929 - 11 Mar 2020

Cited by 5 | Viewed by 3467

Abstract

A terahertz (THz) detector based on thermoelectric thin films was simulated using the finite elements method. The thermoelectric circuit consisted of

S b

and

B i_{88} S b_{12}

150-nm films on the mica substrate.

S b

, [...] Read more.

A terahertz (THz) detector based on thermoelectric thin films was simulated using the finite elements method. The thermoelectric circuit consisted of

S b

and

B i_{88} S b_{12}

150-nm films on the mica substrate.

S b

B i_{88} S b_{12}

, and mica-substrate properties have been measured experimentally in the THz frequency range. The model of electromagnetic heating was used in order to estimate possible heating of

S b

B i_{88} S b_{12}

contact. THz radiation power varied from 1

μ

W to 50 mW, and frequency varied in the range from 0.3 to 0.5 THz. The calculations showed a temperature difference of up to 1 K, voltage up to 0.1 mV, and responsivity of several mVW

^{- 1}

. The results show that thin

S b

and

B i - S b

thermoelectric films can be used for THz radiation detection at room temperatures. Full article

(This article belongs to the Special Issue Terahertz Sensing)

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