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Keywords = emittance anisotropy

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12 pages, 2274 KiB  
Communication
Anisotropic Purcell Effect and Quantum Interference in Fractal Aggregates of Nanoparticles
by Vassilios Yannopapas and Emmanuel Paspalakis
Photonics 2023, 10(8), 898; https://doi.org/10.3390/photonics10080898 - 3 Aug 2023
Viewed by 2096
Abstract
We study theoretically the emergence of an anisotropic Purcell factor in random two-dimensional fractal aggregates of nanoparticles. These nanoparticles can either be metallic nanoparticles made of silver, which exhibit surface plasmon resonances, or high-index dielectric nanoparticles like silicon, which possess optical Mie resonances. [...] Read more.
We study theoretically the emergence of an anisotropic Purcell factor in random two-dimensional fractal aggregates of nanoparticles. These nanoparticles can either be metallic nanoparticles made of silver, which exhibit surface plasmon resonances, or high-index dielectric nanoparticles like silicon, which possess optical Mie resonances. To calculate the spontaneous emission rates of a quantum emitter, we utilize the electromagnetic Green’s tensor within the framework of the coupled-dipole method. Our findings reveal that the Purcell factor exhibits spatial variations, with certain regions, referred to as hot spots, displaying high values for dipoles oriented within the plane of the fractal aggregate, while dipoles oriented vertically to the aggregate have values close to unity. This anisotropy in the Purcell factor leads to significant quantum interference effects in the spontaneous emission paths of multi-level quantum emitters. As a consequence of this quantum interference, we demonstrate the occurrence of population trapping in a V-type quantum emitter embedded within a fractal aggregate of nanoparticles which cannot otherwise take place if the emitter is placed in vacuum. Full article
(This article belongs to the Special Issue Optical Interferometry)
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9 pages, 2400 KiB  
Article
Controlled Spintronic Emitter of THz Radiation on an Atomically Thin WS2/Silicon Substrate
by Arseniy Buryakov, Anastasia Gorbatova, Pavel Avdeev, Nikita Bezvikonnyi, Daniil Abdulaev, Alexey Klimov, Sergei Ovcharenko and Elena Mishina
Metals 2022, 12(10), 1676; https://doi.org/10.3390/met12101676 - 6 Oct 2022
Cited by 9 | Viewed by 2046
Abstract
The control and monitoring of the polarization of terahertz radiation are of interest for numerous applications. Here we present a simple controllable THz emitter with a small coercive magnetic field. It is based on a Co/WS2/silicon structure, in which the presence [...] Read more.
The control and monitoring of the polarization of terahertz radiation are of interest for numerous applications. Here we present a simple controllable THz emitter with a small coercive magnetic field. It is based on a Co/WS2/silicon structure, in which the presence of uniaxial magnetic anisotropy caused by mechanical stress in a ferromagnetic film was found. Our results show that a ferromagnet/semiconductor emitter can become a technologically simple device for terahertz spintronics. Full article
(This article belongs to the Section Crystallography and Applications of Metallic Materials)
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18 pages, 2918 KiB  
Article
Detectability of the Cross-Correlation between CMB Lensing and Stochastic GW Background from Compact Object Mergers
by Giulia Capurri, Andrea Lapi and Carlo Baccigalupi
Universe 2022, 8(3), 160; https://doi.org/10.3390/universe8030160 - 3 Mar 2022
Cited by 8 | Viewed by 2203
Abstract
The anisotropies of the Stochastic Gravitational-Wave Background (SGWB), produced by merging compact binaries, constitute a possible new probe of the Large-Scale Structure (LSS). However, the significant shot noise contribution caused by the discreteness of the GW sources and the poor angular resolution of [...] Read more.
The anisotropies of the Stochastic Gravitational-Wave Background (SGWB), produced by merging compact binaries, constitute a possible new probe of the Large-Scale Structure (LSS). However, the significant shot noise contribution caused by the discreteness of the GW sources and the poor angular resolution of the instruments hampers the detection of the intrinsic anisotropies induced by the LSS. In this work, we investigate the potential of cross-correlating forthcoming high precision measurements of the SGWB energy density and the Cosmic Microwave Background (CMB) lensing convergence to mitigate the effect of shot noise. Combining a detailed model of stellar and galactic astrophysics with a novel framework to distribute the GW emitters in the sky, we compute the auto- and cross-correlation power spectra for the two cosmic fields, evaluate the shot noise contribution and predict the signal-to-noise ratio. The results of our analysis show that the SGWB energy density correlates significantly with the CMB lensing convergence and that the cross-correlation between these two cosmic fields reduces the impact of instrumental and shot noise. Unfortunately, the S/N is not high enough to detect the intrinsic SGWB anisotropies. Nevertheless, a network composed of both present and future generation GW interferometers, operating for at least 10 yrs, should be able to measure the shot noise contribution. Full article
(This article belongs to the Special Issue Cross Correlation of Cosmic Fields: A Powerful Statistical Tool for Astrophysics, Cosmology, and Fundamental Physics)
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14 pages, 659 KiB  
Article
A Laboratory Goniometer System for Measuring Reflectance and Emittance Anisotropy
by Peter P. J. Roosjen, Jan G. P. W. Clevers, Harm M. Bartholomeus, Michael E. Schaepman, Gabriela Schaepman-Strub, Henk Jalink, Rob Van der Schoor and Arjan De Jong
Sensors 2012, 12(12), 17358-17371; https://doi.org/10.3390/s121217358 - 13 Dec 2012
Cited by 21 | Viewed by 10183
Abstract
In this paper, a laboratory goniometer system for performing multi-angular measurements under controlled illumination conditions is described. A commercially available robotic arm enables the acquisition of a large number of measurements over the full hemisphere within a short time span making it much [...] Read more.
In this paper, a laboratory goniometer system for performing multi-angular measurements under controlled illumination conditions is described. A commercially available robotic arm enables the acquisition of a large number of measurements over the full hemisphere within a short time span making it much faster than other goniometers. In addition, the presented set-up enables assessment of anisotropic reflectance and emittance behaviour of soils, leaves and small canopies. Mounting a spectrometer enables acquisition of either hemispherical measurements or measurements in the horizontal plane. Mounting a thermal camera allows directional observations of the thermal emittance. This paper also presents three showcases of these different measurement set-ups in order to illustrate its possibilities. Finally, suggestions for applying this instrument and for future research directions are given, including linking the measured reflectance anisotropy with physically-based anisotropy models on the one hand and combining them with field goniometry measurements for joint analysis with remote sensing data on the other hand. The speed and flexibility of the system offer a large added value to the existing pool of laboratory goniometers. Full article
(This article belongs to the Special Issue Workshop Sensing A Changing World 2012)
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