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Coherent excitation of different resonance modes though selective coupling to odd and even parity multipoles. The coherent spectroscopy uses an optical standing wave as excitation. For a metamaterial at the electric antinode (E-antinode) of the standing wave, its symmetric modes are excited through coupling to even-parity multipoles. Meanwhile, for the same metamaterial at the magnetic antinode (B-antinode), its antisymmetric modes are excited through coupling to odd-parity multipoles.
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Far-field spectroscopy and mapping of electromagnetic near-field distribution are the two dominant tools for analysis and characterization of the electromagnetic response in nanophotonics. Despite the widespread use, these methods can fail at identifying weak electromagnetic excitations masked by stronger neighboring excitations. This is particular...
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Citations
... Plasma nanostructure-based sensors are susceptible to strong electric fields where the analyte is located [6]. However, plasmonic nanostructures suffer from high losses due to the intrinsic absorption of plasmonic metals [7][8][9], which results in a lower quality factor (Q-factor) and limits sensing performance. In recent years, high-refractive index dielectric nanostructures have gained attention in metasurfaces and nanoantennas [10,11] due to their efficient and flexible light control at the nanoscale and their potential for biosensing applications [10,12,13]. ...
We propose an all-dielectric nanorod array for ultra-sensitive refractive index sensing based on quasi-bound states in the continuum (BICs). The nanorod is fabricated by silicon or silicon with an air hole, i.e., the hollow silicon nanorod. The quasi-BICs are formed in the hollow silicon nanorod array due to the symmetry-breaking of air holes. The high-quality factor (Q-factor) and ultra-narrow reflectance spectral width at quasi-BICs contribute to high performances of the sensor. The numerical results show that the sensitivity and figure of merit (FOM) can reach up to 602.9 nm/RIU and 34,977, respectively. The results indicate that the proposed nanostructures of quasi-BICs are promising for advanced biosensing applications.
... Notably, the direction of the electric field vectors in the adjacent square disks are twisting in the opposite directions and produces four longitudinal magnetic moments (white crosses and dots in Figure 1(d)) oriented along the z-axis inversely located in the center of the square disks. The direction arrows of the magnetic fields with head-to-tail links in two pairs form dual parallel magnetic toroidal dipoles [27,28]. Figure 1(e) shows a 3D schematic diagram of the supporting dual parallel magnetic toroidal dipoles (MTD) (the green circular column), which are created by the circular displacement currents (the purple circular column) in the x-y plane. ...
We propose and numerically demonstrate high Q-factor sensors based on all-dielectric metasurfaces, which are very sensitive to the change of the refractive index of the surrounding media and the incident angle. By using the light incident angular scanning method, the all-dielectric metasurface based on symmetric tetramer can act as an excellent sensing platform for trace-amount molecules such as protein A/G, 2, 4-DNT, and 2D material graphene with huge absorbance enhancement in the mid-infrared broadband spectrums. The results reveal that envelope of absorbance amplitudes is in good agreement with the vibrational mode of molecules, and absorbance enhancement factors reach as high as 10 dB in the mid-infrared wavelength range from 5.75 to 6.80 μm. To further increase the Q-factor of the resonances, the all-dielectric metasurface based on asymmetric tetramer is investigated. This asymmetric structure can induce toroidal and magnetic dipoles governed by quasi-BIC to produce multi-extremely narrow linewidth Fano resonances, and the maximum sensitivity reaches up to 1.43 μm/RIU. Therefore, the proposed all-dielectric metasurface demonstrates highly enhanced performance in refractive index and chemical information sensing for trace-amount biomolecules, which inspires the development of new high-sensitivity refractive index sensors for the nondestructive identification in the mid-infrared regime.
... They are now recognized as indispensable contributors to the linear and nonlinear optical properties of matter 10,11 . As such, new types of spectroscopy, including atomic spectroscopy 12 , that are selective to the optical transitions enabled by toroidal dipoles are being developed based on solvatochromism 13 and standing-wave illumination 14 . Furthermore, dynamic anapoles, co-located non-radiating configurations of oscillating electric and toroidal dipoles 2 , are attracting interest as a vehicle for high-quality resonant devices [15][16][17] , quantum qubits 18 and even reservoirs of dark energy 19 . ...
Transverse electromagnetic waves are important carriers of information and energy. In 1996, Hellwarth and Nouchi theoretically identified a radically different, non-transverse type of electromagnetic pulse with a toroidal topology. These pulses, which are propagating counterparts of localized toroidal dipole excitations in matter, exhibit unique electromagnetic wave properties and, so far, have never been experimentally realized and observed. Here we report the generation of such toroidal light pulses in the optical and terahertz regions by the use of tailored nanostructured meta-surfaces. This achievement paves the way for experimental studies of energy and information transfer with toroidal light pulses, their space–time coupling and their light–matter interactions involving anapoles, localized space–time coupled excitations, skyrmions and toroidal qubits, which are of growing interest for the fundamental science of light and applications. Pulses of light with a toroidal structure are experimentally realized in the terahertz and optical regions.
... Low concentrations of chemical biomolecules or even single molecules can be detected by them [2]. Unfortunately, plasmonic nanostructures have very high losses because of the intrinsic absorption of plasmonic metals [3][4][5], which represents a lower quality factor (Q-factor) and limits the sensing performance. Compared to plasmonic nanostructures, dielectric nanostructures do not suffer from absorption losses. ...
The electromagnetic fields distributed on the surface region of the nanostructure is very important to improve the performance of the sensor. Here, we proposed a highly sensitive sensor based on toroidal dipole (TD) governed by bound state in the continuum (BIC) in all-dielectric metasurface consisting of single non-coaxial core-shell cylinder nanostructure array. The excitation of TD resonance in a single nanostructure is still challenging. The designed nanostructure not only supports TD resonance in a single nanostructure but also has very high Q-factor. More importantly, its electric field distributes at the surface of outer cylinder-shell, which is very suitable for biosensing. To evaluate the sensing performance of our proposed structure, we investigated the sensitivity and the figure of merit (FOM) of nanostructure with different structural parameters. Maximum sensitivity and FOM can reach up to 342 nm/RIU and 1295 when the asymmetric parameter d =10 nm. These results are of great significance to the research of TD resonance and the development of ultrasensitive sensor.
... Compared to tuning the optical nonlinearity of reconfigurable metasurfaces, this method can work with arbitrarily low intensity even down to single-photon regime [151], as long as their relative phase and intensity have a desired difference. Coherent control on ultrathin metasurfaces leads to various optical phenomena and practical applications, including ultrafast modulation [150,152,153], data and image processing [154][155][156][157], polarisation control [158], selective-excitation spectroscopy [159,160] and wavefront control [161][162][163]. ...
... The nodes/antinodes of the electric and magnetic fields are out of phase, which means that the electric field antinodes spatially correspond to the magnetic field nodes and vice versa. The vanishing points of standing wave electric/magnetic field allows selectively exciting multipolar resonances that can only be excited by the electric/magnetic field [159], and revealing high-order resonances that are invisible under travelling wave illumination [160]. Figure 2.14b and c demonstrate the enhancement/suppression of electric and magnetic dipole resonances of ultrathin metasurfaces, through the indication of their coherent absorption spectra. ...
... In the former case, we demonstrate selective excitation of plasmonic resonances along with the recently demonstrated work in literature [159,160]. This analysis forms the theoretical foundation of the thesis, which also represents a significant step towards the practical applications of coherent illumination spectroscopy, which up to now has been limited to ultrathin membrane substrates. ...
The optical properties of materials can manifest differently in traveling and standing light waves. In standing waves, “coherent control” of the energy exchange between incident and scattered waves enables control of light with light without nonlinearity, at arbitrarily low intensity and on ultrashort (few optical cycle) timescales. This thesis reports on my research efforts towards application of coherent control techniques for shaping the wavefronts of light scattered by planar photonic metasurfaces: I show for the first time that the coherent control paradigm can be applied to optically thick and/or asymmetric sample/device structures, where previously only vanishingly thin (subwavelength thickness) structures were considered. I have derived the requisite illumination conditions for electric and magnetic field standing wave excitation of substrate-supported (e.g. at an air-glass substrate) meta surface structures; and numerically demonstrated applications to selective excitation spectroscopy and for thin film characterisation. I have introduced a new mechanism for active tuning of gradient index meta surfaces via coherent control of the phase gradient itself – turning what is conventionally a constant in the Generallized Snell’s law into a variable. This is demonstrated in the development of a meta surface design providing, through coherent selective excitation of Mie-type resonances in Si nano-pillars, coherently controlled beam steering (with no moving parts) over a continuous 9.1° range. I have also discussed its potential use for solid state Lidar.
... They are now recognized as indispensable contributors to the linear and nonlinear optical properties of matter [10,11]. As such, new types of spectroscopy, selective to optical transitions enabled by toroidal dipoles, are being developed based on solvatochromism [12] and standing wave illumination [13]. Furthermore, dynamic anapoles, co-located non-radiating configurations of oscillating electric and toroidal dipoles [2] now attract growing interest as a vehicle for high quality resonant devices [14][15][16], quantum qubits [17] and even reservoirs of dark energy [18]. ...
The transverse electromagnetic waves are major information and energy carriers. In 1996, Hellwarth and Nouchi theoretically identified a radically different, non-transverse type of electromagnetic pulses of toroidal topology. These pulses, which are propagating counterparts of localized toroidal dipole excitations in matter and exhibit unique electromagnetic wave properties, have never been observed before. Here, we report the generation and characterization of such optical and terahertz Toroidal Light Pulses (TLPs), launched from tailored nanostructured metasurfaces comprising toroidal emitters. This achievement paves the way for experimental studies of energy and information transfer with TLPs, their space-time "entanglement", and their light-matter interactions involving anapoles, localized space-time entangled excitations, skyrmions, and toroidal qubits that are of growing interest for the fundamental science of light and applications.
... It is noted that the dielectric mode combining with SPPs fields improves the field confinement and thus causes the high transmittance at 0.195 THz and 0.345 THz. Figure 5(a) clearly shows that the resonant mode at 0.176 THz is a pure symmetric mode, where the charge distributions in the two metal grating layers are identical. However, as shown in Fig. 5(b), the resonance at 0.332 THz is a anti-symmetric mode, where the charge distributions in the two metal grating layers have opposite signs [49]. We also simulated the electric field vector of 0.176 and 0.332 THz for the CPS. ...
One composite plasmonic slab with a broad bandgap (40%) is experimentally and numerically demonstrated in the terahertz (THz) region. The composite slab consists of double-layer metallic gratings and a dielectric film, which supports two resonant modes. Electric field vectors and charge distributions proved that the low-frequency resonant mode originates from the symmetric plasmonic mode, while the high-frequency resonant mode is induced by the hybrid mode of plasmonic and dielectric modes. Compared with the double-layer metallic grating, the inserted dielectric film significantly enhances the transmission of the transverse magnetic (TM) waves and induces Fano resonances. The near-field coupling between metal gratings and dielectric film can be manipulated by changing the thickness and the refractive index of dielectric films. We further demonstrated that the plasmonic bandgap can be manipulated by tuning the grating width. These results suggest that this composite plasmonic slab is promising in terahertz integrated components development such as a filter, polarizer, or sensor.
... Moreover, this perfect absorption can be tuned from 100% to 0% just by changing the relative phase of the incident light, indicating ultrahigh modulation depth [41,42]. CPA was first realized in a silicon slab [34], and until then, different materials were used, including silicon and silica composite cavities [29,43], metamaterials [44][45][46][47][48] and so on [49,50]. Coherent absorption provides a new way to enhance and modulate light absorption of graphene and a number of studies has been carried out [51][52][53][54][55][56][57][58]. ...
We show numerically and theoretically that coherent perfect absorption can be achieved in suspended monolayer graphene with ultra-broad bandwidth from visible to near-infrared range under oblique incidence. The absorption can be tuned from 0% to 100% by controlling the relative phase of the coherent incident light, showing great capacity in absorption modulation. We also studied tunable coherent absorption of graphene placed in high refractive index media with a gap (symmetrically based graphene), finding that graphene keeps high absorption (over 90%) with near-infrared light, and the maximum absorption wavelength is determined by the thickness of the gap. The broadband and high tunable absorption in graphene in the visible and near-infrared light will provide an efficient way to manipulate the interaction between light and graphene and serve applications in optical modulators, transducers, sensors and coherent detectors. Moreover, this absorption enhancement theory also applies to other 2D materials including black phosphorus, MoS2 and so on.
... For a long time, dynamic, i.e., time-varying anapoles remained a theoretical concept. Their existence was first demonstrated in a microwave metamaterial [10] and has since been repeated in a variety of man-made systems in various domains of the electromagnetic spectrum [8,[11][12][13][14][15][16][17]. From the general properties of nonradiating configurations it is relatively simple to show that any nonradiating configuration can be regarded as a collection of anapoles [1,18,19]. ...
... Due to the linearity of Maxwell's equations the radiation pattern of the accelerated point particle with an anapole moment can be obtained by combining Eqs. (17), (18), (20), and (21) with Eq. (3). After some simplification one can show that the far-field zero-velocity radiation of a point particle with an anapole moment is as follows: ...
... Using Eq. (25) and the time-harmonic versions of Eqs. (17) and (20), the ellipticity of the radiation from accelerated electric (χ (p) ) and toroidal (χ (T ) ) dipoles can be shown to be as follows: ...
Emission of electromagnetic radiation by accelerated particles with electric, toroidal, and anapole dipole moments is analyzed. It is shown that ellipticity of the emitted light can be used to differentiate between electric and toroidal dipole sources and that anapoles, elementary neutral nonradiating configurations, which consist of electric and toroidal dipoles, can emit light under uniform acceleration. The existence of nonradiating configurations in electrodynamics implies that it is impossible to fully determine the internal makeup of the emitter given only the distribution of the emitted light. Here we demonstrate that there is a loop hole in this “inverse source problem.” Our results imply that there may be a whole range of new phenomena to be discovered by studying the electromagnetic response of matter under acceleration.
... This kind of transistors is attractive in quantum computing and data transferring systems, so numerous attempts to provide practical transistors of this type have taken place in recent years [16][17][18][19][20][21] . In addition, some novel appli- cations based on this method, like more accurate spectroscopy and localized absorption in metamaterials have been established [22][23][24] . When we benefit from the coherency of light, interference can help to achieve intensive interaction. ...
This study aims to design an all-optical transistor based on tunneling of light through frustrated total internal reflection. Under total internal reflection, the electromagnetic wave penetrates into the lower index medium. If a medium with high refractive index is placed close to the boundary of the first one, a portion of light leaks into the second medium. The penetrated electromagnetic field distribution can be influenced by another coherent light in the low refractive index medium via interference, leading to light amplification. Upon this technique, we introduce coherent all-optical transistors based on photonic crystal structures. Subsequently, we inspect the shortest pulse which is amplified by the designed system and also its terahertz repetition rate. We will show that such a system can operate in a cascade form. Operating in terahertz range and the amplification efficiency of around 20 are of advantages of this system.
