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Lee HT, Kim J, Lee JS, Yoon M, Park HR. More Than 30 000-fold Field Enhancement of Terahertz Nanoresonators Enabled by Rapid Inverse Design. NANO LETTERS 2023; 23:11685-11692. [PMID: 38060838 DOI: 10.1021/acs.nanolett.3c03572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2023]
Abstract
The rapid development of 6G communications using terahertz (THz) electromagnetic waves has created a demand for highly sensitive THz nanoresonators capable of detecting these waves. Among the potential candidates, THz nanogap loop arrays show promising characteristics but require significant computational resources for accurate simulation. This requirement arises because their unit cells are 10 times smaller than millimeter wavelengths, with nanogap regions that are 1 000 000 times smaller. To address this challenge, we propose a rapid inverse design method using physics-informed machine learning, employing double deep Q-learning with an analytical model of the THz nanogap loop array. In ∼39 h on a middle-level personal computer, our approach identifies the optimal structure through 200 000 iterations, achieving an experimental electric field enhancement of 32 000 at 0.2 THz, 300% stronger than prior results. Our analytical model-based approach significantly reduces the amount of computational resources required, offering a practical alternative to numerical simulation-based inverse design for THz nanodevices.
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Affiliation(s)
- Hyoung-Taek Lee
- Department of Physics, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, South Korea
| | - Jeonghoon Kim
- Department of Physics, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, South Korea
| | - Joon Sue Lee
- Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Mina Yoon
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Hyeong-Ryeol Park
- Department of Physics, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, South Korea
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Kim S, Kim D, Lee Y, Lee G, Jeong J, Lee D, Kim DS. Broadband high-performance terahertz polarizer based on a dense array of 5 nm gap slit antennas. OPTICS EXPRESS 2022; 30:30038-30046. [PMID: 36242115 DOI: 10.1364/oe.460859] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 07/17/2022] [Indexed: 06/16/2023]
Abstract
Critical factors for terahertz polarizers include broadband operation, high transmittance, and a good extinction ratio. In this paper, using a 5 nm-wide metallic slit array with a 200 nm periodicity as a wire grid polarizer, we achieved over 95% transmittance with an average extinction ratio of 40 dB, over the entire spectrum as defined by the terahertz time-domain spectroscopy (0.4 ∼ 2 THz). Theoretical calculations revealed that the slit array can show 100% transmission up to 5 THz, and wider bandwidths with a higher cutoff frequency can be achieved by reducing the slit periodicity. These results provide a novel approach for achieving a broadband THz polarizer and open a new path for seamless integration of the polarizers with nanophotonic applications.
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Park HR, Namgung S, Chen X, Oh SH. High-density metallic nanogap arrays for the sensitive detection of single-walled carbon nanotube thin films. Faraday Discuss 2015; 178:195-201. [DOI: 10.1039/c4fd00233d] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have investigated the extraordinary optical transmission of terahertz waves through an array of nanogaps with varying dimensions and periodicities, and used this platform to demonstrate terahertz sensing of a thin film of single-walled carbon nanotubes. We have used atomic layer lithography to fabricate periodic arrays of nanogap loops that have a gap size of 2 nm and a loop length of 100 μm (aspect ratio of 50 000). These sub-mm-scale loops of nanogaps can sustain terahertz electromagnetic resonances along the contour. We have characterized the transmission of terahertz waves through the nanogap arrays and investigated the influence of inter-gap electromagnetic coupling as the array periodicity shrinks from 100 μm to 4 μm. While the gaps occupy only 0.1% of the surface area, we have measured an amplitude (|E|) transmittance of over 50% due to the strong and broadband field enhancement inside the nanogaps. The absolute transmission through the 2 nm gaps along the rectangular loops can be boosted up to 25%, while it is only 1% for annular gaps with the same perimeter. Furthermore, the extremely tight field confinement and strong field enhancement near the 2 nm gap lead to 43% extinction of THz waves in a 10 nm-thick film of single-walled carbon nanotubes over the gaps. On the other hand, THz extinction by the same nanotube film on a bare glass substrate is only 2%. These nanogaps pave the way toward developing sensitive terahertz detectors for biological and chemical targets.
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Affiliation(s)
- Hyeong-Ryeol Park
- Department of Electrical and Computer Engineering
- University of Minnesota
- Minneapolis
- USA
| | - Seon Namgung
- Department of Electrical and Computer Engineering
- University of Minnesota
- Minneapolis
- USA
| | - Xiaoshu Chen
- Department of Electrical and Computer Engineering
- University of Minnesota
- Minneapolis
- USA
| | - Sang-Hyun Oh
- Department of Electrical and Computer Engineering
- University of Minnesota
- Minneapolis
- USA
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Yang M, Li TF, Sheng QW, Guo TJ, Guo QH, Cui HX, Chen J. Manipulation of dark photonic angular momentum states via magneto-optical effect for tunable slow-light performance. OPTICS EXPRESS 2013; 21:25035-25044. [PMID: 24150346 DOI: 10.1364/oe.21.025035] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We propose a novel scheme in realizing tunable slow-light performance by manipulating dark photonic angular momentum states (PAMSs) in metamaterials via the magneto-optical effect. We show that by applying a static magnetic field B, some pairs of sharp transmission dips can be observed in the background transparency window of a complex metamaterial design. Each pair of transmission dips are related to the excitation of dark PAMSs with opposite topological charges -m and +m, with a lifted degeneracy due to the classic analogue of Zeeman effect. Nonreciprocal characteristics can be observed in the distributions of field amplitude and transverse energy flux. The performance of slow light, including the group index ng, its abnormal feature, the associated strong absorption and the dependence with B are also discussed.
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Park HR, Ahn KJ, Han S, Bahk YM, Park N, Kim DS. Colossal absorption of molecules inside single terahertz nanoantennas. NANO LETTERS 2013; 13:1782-1786. [PMID: 23441747 DOI: 10.1021/nl400374z] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Molecules have extremely small absorption cross sections in the terahertz range even under resonant conditions, which severely limit their detectability, often requiring tens of milligrams. We demonstrate that nanoantennas tailored for the terahertz range resolves the small molecular cross section problem. The extremely asymmetric electromagnetic environment inside the slot antenna, which finds the electric field being enhanced by thousand times with the magnetic field changed little, forces the molecular cross section to be enhanced by >10(3) accompanied by a colossal absorption coefficient of ~170,000 cm(-1). Tens of nanograms of small molecules such as 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and lactose drop-cast over an area of 10 mm(2), with only tens of femtograms of molecules inside the single nanoslot, can readily be detected. Our work enables terahertz sensing of chemical and biological molecules in ultrasmall quantities.
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Affiliation(s)
- Hyeong-Ryeol Park
- Center for Subwavelength Optics, Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
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Razzari L, Toma A, Clerici M, Shalaby M, Das G, Liberale C, Chirumamilla M, Zaccaria RP, De Angelis F, Peccianti M, Morandotti R, Di Fabrizio E. Terahertz Dipole Nanoantenna Arrays: Resonance Characteristics. PLASMONICS (NORWELL, MASS.) 2013; 8:133-138. [PMID: 23504505 PMCID: PMC3597338 DOI: 10.1007/s11468-012-9439-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Accepted: 08/13/2012] [Indexed: 05/10/2023]
Abstract
Resonant dipole nanoantennas promise to considerably improve the capabilities of terahertz spectroscopy, offering the possibility of increasing its sensitivity through local field enhancement, while in principle allowing unprecedented spatial resolutions, well below the diffraction limit. Here, we investigate the resonance properties of ordered arrays of terahertz dipole nanoantennas, both experimentally and through numerical simulations. We demonstrate the tunability of this type of structures, in a range (∼1-2 THz) that is particularly interesting and accessible by means of standard zinc telluride sources. We additionally study the near-field resonance properties of the arrays, finding that the resonance shift observed between near-field and far-field spectra is predominantly ascribable to ohmic damping.
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Affiliation(s)
- Luca Razzari
- Fondazione Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy
| | - Andrea Toma
- Fondazione Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy
| | - Matteo Clerici
- INRS-EMT, 1650 Boulevard Lionel Boulet, Varennes, Québec Canada J3X 1S2
| | - Mostafa Shalaby
- INRS-EMT, 1650 Boulevard Lionel Boulet, Varennes, Québec Canada J3X 1S2
| | - Gobind Das
- Fondazione Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy
| | - Carlo Liberale
- Fondazione Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy
| | | | | | | | - Marco Peccianti
- INRS-EMT, 1650 Boulevard Lionel Boulet, Varennes, Québec Canada J3X 1S2
| | | | - Enzo Di Fabrizio
- Fondazione Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy
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Jain S, Parashar J, Kurchania R. Effect of magnetic field on terahertz generation via laser interaction with a carbon nanotube array. INTERNATIONAL NANO LETTERS 2013. [DOI: 10.1186/2228-5326-3-1] [Citation(s) in RCA: 166] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Razzari L, Toma A, Shalaby M, Clerici M, Zaccaria RP, Liberale C, Marras S, Al-Naib IAI, Das G, De Angelis F, Peccianti M, Falqui A, Ozaki T, Morandotti R, Di Fabrizio E. Extremely large extinction efficiency and field enhancement in terahertz resonant dipole nanoantennas. OPTICS EXPRESS 2011; 19:26088-94. [PMID: 22274197 DOI: 10.1364/oe.19.026088] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The distinctive ability of nanometallic structures to manipulate light at the nanoscale has recently promoted their use for a spectacular set of applications in a wide range of areas of research including artificial optical materials, nano-imaging, biosensing, and nonlinear optics. Here we transfer this concept to the terahertz spectral region, demonstrating a metal nanostructure in shape of a dipole nanoantenna, which can efficiently resonate at terahertz frequencies, showing an effective cross section >100 times larger than its geometrical area, and a field enhancement factor of ~280, confined on a lateral section of ~λ/1,000. These results lead to immediate applications in terahertz artificial materials exhibiting giant dichroism, suggest the use of dipole nanoantennas in nanostructure-based terahertz metamaterials, and pave the way for nanoantenna-enhanced terahertz few-molecule spectroscopy and localized terahertz nonlinear optics.
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Affiliation(s)
- Luca Razzari
- Fondazione Istituto Italiano di Tecnologia, Genova, Italy.
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Shu J, Qiu C, Astley V, Nickel D, Mittleman DM, Xu Q. High-contrast terahertz modulator based on extraordinary transmission through a ring aperture. OPTICS EXPRESS 2011; 19:26666-26671. [PMID: 22274251 DOI: 10.1364/oe.19.026666] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We demonstrated extraordinary THz transmission through ring apertures on a metal film. Transmission of 60% was obtained with an aperture-to-area ratio of only 1.4%. We show that the high transmission can be suppressed by over 18 dB with a thin layer of free carriers in the silicon substrate underneath the metal film. This result suggests that CMOS-compatible terahertz modulators can be built by controlling the carrier density near the aperture.
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Affiliation(s)
- Jie Shu
- Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA
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Park HR, Bahk YM, Ahn KJ, Park QH, Kim DS, Martín-Moreno L, García-Vidal FJ, Bravo-Abad J. Controlling terahertz radiation with nanoscale metal barriers embedded in nano slot antennas. ACS NANO 2011; 5:8340-8345. [PMID: 21961910 DOI: 10.1021/nn2031885] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Nanoscale metallic barriers embedded in terahertz (THz) slot antennas are shown to provide unprecedented control of the transition state arising at the crossover between the full- and half-wavelength resonant modes of such antennas. We demonstrate strong near-field coupling between two paired THz slot antennas separated by a 5 nm wide nanobarrier, almost fully inducing the shift to the resonance of the double-length slot antenna. This increases by a factor of 50 the length-scale needed to observe similar coupling strengths in conventional air-gap antennas (around 0.1 nm), making the transition state readily accessible to experiment. Our measurements are in good agreement with a quantitative theoretical modeling, which also provides a simple physical picture of our observations.
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Affiliation(s)
- Hyeong-Ryeol Park
- Center for Subwavelength Optics, Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
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Wei Z, Cao Y, Fan Y, Yu X, Li H. Broadband transparency achieved with the stacked metallic multi-layers perforated with coaxial annular apertures. OPTICS EXPRESS 2011; 19:21425-21431. [PMID: 22108992 DOI: 10.1364/oe.19.021425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
It is generally believed that, in the phenomena of extraordinary optical transmission, perfect transparency only occurs at a single or a multiple of discrete frequencies. This report presents for the first time that a stacked metallic multi-layered system, being perforated with coaxial annular apertures (CAAs), can be perfectly transparent in a broad frequency range. The phenomenon arises from the coupling of guided resonance modes in CAAs among different metallic layers. The transparency bandwidth is extended to about 40% of the central frequency with only 2-3 metallic layers. Measured transmission spectra in microwave regime are in good agreement with calculations which are semi-analytically resolved by modal expansion method.
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Affiliation(s)
- Zeyong Wei
- Tongji University, Shanghai, 200092, China
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