Dielectric mesoscale spheres have aroused strong interest because of their potential to localize light at deep subwavelength volume and to yield extremal internal magnetic and/or electric field enhancements. Recently, it was showed that such particle could support high-order Mie resonance modes with giant field localization and enhancement. Optimizing the internal fields appears as a key challenge for enhancing wave matter interactions in dielectric mesoscale particles. However, a dielectric particle is always located in some medium, and not in a vacuum. Moreover, the question is how much the environment medium affects the internal field intensities enhancement in the super-resonance effect. Based on Mie theory we show for the first time that the presence of the environment leads to a significant decrease in the intensity of the field in the particle. Thus, the study of the effect of super-resonance becomes meaningless without taking into account the environment. However, a greater enhancement of the internal field is found for the blue-shifted Mie size parameter of the sphere when the particle, for example, is in air rather than in vacuum.
Some new unusual physical phenomena and effects associated with dielectric mesoscale particles with typical Mie size parameter around 10 were studied and have been discovered during the last decade. There are: optical nanovortices; anapoles; photonic nanojets and terajets as in transmission as in reflection modes; structured fields in the form of photonic hooks and loops with subwavelength curvature; effects of anomalous apodization; high-order Fano resonances; effects associated with the generation of extreme magnetic and acoustic fields; effects of overcoming the diffraction limit; anomalous Gouy phase shift; flat focusing mirrors, and others. This brief review presents the authors’ approach to these problems. The focus of this review is on structural design, numerical simulation, demonstration of new concepts and functionalities, application of the proposed principles in devices. The presence of a number of interesting applications in optics, terahertz, acoustics and plasmonics indicates that in optics, terahertz, acoustics and plasmonics a new promising direction arose, which can be called as “mesotronics”.
Some new unusual physical phenomena and effects associated with dielectric mesoscale particles with Mie size parameter near 10 were studied and have been discovered during the last decade. In this paper, we propose nanoholes structured wavelength-scaled dielectric cubic particle with refractive index near two, where the array of nanoholes can act as a plurality of near-field probes to simultaneously illuminate the sample surface and it has the potential of surpassing the performance of most existing nearfield imaging approaches. We also offer the concept of the single nano-structuring of a dielectric cylinder or sphere made from conventional optical materials. The choice of the diameter of the nanohole in the particle "transfers" it into the resonance mode, when the characteristics of the field localized in the shadow part of the particle are determined not by the wavelength, but by the size of the nanohole. Thus, the diameter of the focused spot at the exit from the particle can be much smaller than the solid immersion diffraction limit.
The optical spin torque (OST) exerted on a dielectric Rayleigh spherical particle by photonic hook is investigated in the framework of dipole approximation. Optical spin torque is a type of optical torque that causes a particle to rotate around its center of mass. I.V. Minin and O.V.Minin discovered the photonic hook phenomenon in 2015 (Patent of Russia 161207). They used the combined structure of cube and prism to form a curved beam to pull a small particle, which caused a great sensation in the field of photonics. In this paper, the photonic hook is generated by a plane wave illuminating a dielectric irregular cuboid with one corner cut off. The effects of wavelength and slope of cutting of the irregular cuboid on the OST are analyzed. The numerical results show that the wavelength and inclination of cutting greatly affect the OST. Optical spin torques contain a large amount of negative torques and are sensitive to the slope of cutting of the irregular cuboid. The results of this paper are expected to provide theoretical support for the manipulation and rotation of Rayleigh particles in structured wavelength-scaled localized beams.
Some new unusual physical phenomena and effects associated with dielectric mesoscale particles with Mie size parameter near 10 were studied and have been discovered during the last decade. There are: photonic nanojets; terajets as in transmission as in reflection modes; structured fields in the form of photonic hooks and loops; optical nanovortices, effects of anomalous apodization; high-order Fano resonances; effects associated with the generation of giant magnetic and acoustic fields, effects of overcoming the diffraction limit, anomalous Gouy phase shift, flat focusing mirrors, anapoles and others. This brief review presents the authors’ approach to these problems.
In the past few years, it has shown that photonic jet – a high-intensity near-field focus can be curved through focusing of an asymmetric mesoscale dielectric particle. This unique electromagnetic beam configuration breaking spatial symmetry was termed ‘photonic hooks’ and demonstrated different features from Airy-family beams using a relatively simple experimental setup. The measured radius of the photonic curvature it creates approximates to half of the wavelength, which is the smallest curvature of electromagnetic wave ever reported. This effect was discovered in many relevant fields, including near-field optics (both in transmitted and reflection modes), terahertz (THz) radiation, in-plane plasmonics, and acoustics, and this paper is a short review for them.
We report on our recent approaches focused on the formation of a new class of subwavelength scale self-bending light beams, discovered in 2015, in application to in-plane surface plasmon. For the particle with broken symmetry (Janus particle) the morphology of the field localization area depends on the orientation of the particle that resembles the two faces of “Janus bifrons”. Photonic hook (PH) light do not propagate along straight line but instead follow curved trajectory. Wavefront analysis of such asymmetric mesoscale structure reveals that the unequal phase of the transmitted plane wave results in the irregularly concave deformation of the wavefront inside the structure that then leads to creation of the PH. Such dielectric structures enabling the realization of ultracompact wavelength-scaled and wavelength selective new inplane nanophotonic components.
I. Minin, O. Minin, J. Salvador-Sánchez, J. Delgado-Notario, J. Calvo-Gallego, P. F. Baranov, M. Ferrando-Bataller, K. Fobelets, J. Velázquez-Perez, Y. Meziani
In the present work, we report on resolution enhancement of a terahertz imaging system using the terajet effect. A wavelength-scaled particle (a Te on cube for simplicity) was used to localize incident radiation to a subwavelength volume and focus it directly onto the objects under imaging. A strained-silicon modulation field effect transistor was used as a direct detector of an incident terahertz beam at 0.3 THz. At first, the terahertz imaging of the objects was performed without the cube. A clear enhancement of the resolution of the terahertz image was obtained when the cube was placed in the focal point of the terahertz beam in front of the object of interest.
The parameters that determine the manipulation of nanoparticles depend on the parameters of the illuminating optical field. This leads to a number of fundamental limitations. For example, the power is limited by the incident wavelength. However, there are several ways to work around these limitations. In this article, we demonstrate that the optical power acts on a nanoparticle placed near a hole made in the shadow surface of a dielectric particle of wavelength dimensions and with a refractive index contrast of 1.8 like an optical magnet, and the nanoparticle is moved into the nanohole. Numerical simulations show that light can be trapped inside a nanohole even when the hole size is only λ/100 and therefore the optical magnet can attract nanoparticles at least of the same size. The use of such an optical magnet is of interest primarily for surface cleaning and biomedical applications.
We demonstrate the concept of fiber-based terahertz hook. The subwavelength photonic hook is obtained in the vicinity of a shaped fiber tip with asymmetric radiation. A 193 THz continuous-wave source, commonly used for medical imaging, has been required. Photonic hook with a lateral feature size less than the half-wavelength is achieved using a hemispherical shaped fiber tip with metallic mask. This breakthrough is carried out in ambient air by using a 2.58λ - diameter fiber with a shaped tip (λ is a radiation wavelength). A good correlation is observed between the computed intensity distribution of photonic hook and the tip sizes. Photonic hook generated with a shaped fiber tip, easier to manipulate, shows far-reaching benefits for potential applications such as ophthalmic laser surgery, super-resolution microscopy, photolithography, and material processing.
The aim of this investigation is to search for the possibility of terahertz (THz) spectroscopy in combination with dielectrophoresis for studying erythrocytes from patients with diffuse liver diseases for diagnostics and differentiation of liver fibrosis degrees. Seventy-nine men aged 33 to 67 years with diffuse liver pathology, mainly alcohol, viral, and mixed genesis with varying degrees of liver fibrosis, were included in the study with 30 men (31- to 64-year-old) without signs of pathology of internal organs and liver fibrosis (F0, first group). The study of suspensions of red blood cells was carried out by THz spectroscopy and dielectrophoresis. An increase in the degree of liver fibrosis was associated with an increase in the number of deformed cells prone to aggregation and destruction, with a reduced surface charge, thickened membranes with high electrical conductivity, low deformability on the background of high summarized viscosity, and rigidity indicators (p < 0.0001 to 0.05). Strong correlations of THz spectroscopy indices with electrical and viscoelastic parameters of red blood cells were obtained. The revealed possibilities of the study of blood and its cell components are very promising in the diagnosis and differentiation of the degrees of liver fibrosis.
A simple millimeter wave and terahertz (THz) receiver scheme that uses subwavelength focusing of electromagnetic beam on the point-contact detector area with waveguide dimensions is studied. A detection system with such an optical coupling scheme is implemented, where the signal to be detected is coupled to a detector through a mesoscale dielectric particle lens based on terajet effect. We have experimentally demonstrated an enhancement of the point-contact detector sensitivity higher than 6 dB and with 1.5 times decreasing of the noise equivalent power value. The results show that the proposed method could be applied to reduce the size and increase the sensitivity of various THz systems, including imaging, which would enable significant progress in different fields such as physics, medicine, biology, astronomy, etc.
The mechanism of formation of a terahertz jet by a dielectric cuboid and a sphere surrounded by ideally conducting screens is considered. The maximum screen influence is observed when the screen is located near the alight cuboid base. The screen influence eases when the screen is shifting along the dielectric object. Power flux density localization area is almost completely shifted inside the object when the screen is situated in the center. The minimum influence is observed when screen placed in the shadow plane of the cuboid base. This effect caused by the screen influence on electric field component tangential to the side edges and thus on the power flux directed to the central axis of the object. The screen influence on the terahertz jet in spherical object has been compared. Value of the power flux density after passing the object is higher in a cuboid, but the focusing characteristics are better (appearing on shorter distances) in a sphere.
During last several years it was shown, that an electromagnetic field can be made to curve after propagation through a simple dielectric mesoscale Janus particle of special shape, which adds a newfound degree of simplicity. This effect was discovered by I.V.Minin and O.V.Minin and termed ‘photonic hooks’– it is an unique electromagnetic self-bending subwavelength structured light beams configuration behind a mesoscale particle with a broken symmetry and differ from Airy-family beams. PH features the radius of curvature, which is about 2 times smaller than the electromagnetic wavelength - this is the smallest curvature radius of electromagnetic waves ever reported. The nature of a photonic hook is in dispersion of the phase velocity of the waves inside of particle, resulting in interference. Here, we report an experimental verification of the photonic hook effect in terahertz waveband.
The diffraction limit of electromagnetic waves restricts the formation of sub-wavelength spots. The feasibility to generate scattered beams of light with a high-intensity main lobe, a weak sub-diffracting waist, and a very low divergence angle, named Photonic nanojets, was demonstrated traditionally with spherical particles. Various practical applications require the creation of different types of photonic jets or electromagnetic streams with specific characteristics and properties. For instance, photonic jets can be applied to ease the coupling into the optical waveguides. In this case, photonic jets play the role of a coupling element similar to the lens, grating coupler or prism. To address this challenge, we study the Fresnel Zone Plate (FZP) of rings-like shape. We show that the Babinet principle can be applied for studying the complementary diffractive structures for the formation of near-field photonic jets on a facet of the optical waveguide. Using COMSOL Multiphysics, we built a model of the Fresnel Zone Plate structure based on rings and demonstrate the applicability of Babinet’s principle for the formation of photonic jets in the near-infrared.
The spectral and amplitude-frequency characteristics of a new pyroelectric detector based on thin tetraaminodiphenyl polycyclic polymer films with a thickness of <1 μm were studied in the electromagnetic radiation ranges of 0.4 to 10 and 300 to 3000 μm and at local wavelengths of 81 and 100 μm, respectively. It is shown that the volt–watt sensitivity of such a detector in the entire range is practically nonselective and is 2 to 10 times higher than the sensitivity of other pyroelectric detectors and the Golay cell. The bandwidth of the proposed pyrodetector was 330 to 500 Hz. The results showed good prospects of these sensors for fast ultrawideband spectroscopy, covering visible, infrared, terahertz, and millimeter wave ranges.
We introduce a novel phase-only diffractive optical element called chiral binary square axicon (CBSA). The CBSA is designed by linearly rotating the square half-period zones of the binary square axicon with respect to one another. A quadratic phase mask (QPM) is combined with the CBSA using modulo-2π phase addition technique to bring the far-field intensity pattern of CBSA at the focal plane of the QPM and to introduce quasiachromatic effects. The periodically rotated zones of CBSA produce a whirlpool phase profile and twisted intensity patterns at the focal plane of QPM. The degree of twisting seen in the intensity patterns is dependent upon the angular step size of rotation of the zones. The intensity pattern was found to rotate around the optical axis along the direction of propagation. The phase patterns of CBSA with different angles of zone rotation are displayed on a phase-only spatial light modulator, and the experimental results were found to match with the simulation results. To evaluate the optical trapping capabilities of CBSA, an optical trapping experiment was carried out and the optical fields generated by CBSA were used for trapping and rotating yeast cells.
In this paper, we present the step-index sapphire fiber, applied as a THz probe. The low THz attenuation of sapphire makes it attractive for fabrication of THz optical components. Moreover, it has a high refractive index in THz range, which guarantees a strong modal confinement in a fiber core. The advantages of the edge-defined film-fed growth (EFG) technique allow for fabrication of fibers with close-to-cylindrical shape, the length of 1 m and longer, and the subwavelength diameter of 150 − 400 μm. In order to improve the coupling efficiency, the fiber has polished flat ends. We apply the fabricated 300-μm-diameter sapphire fiber for the THz near-field scanning-probe microscopy. The spatial resolution of our experimental setup is defined by the fiber diameter, thus, it reaches ~ λ/4 for the radiation wavelength λ = 1200 μm. The obtained images of the test objects demonstrate the advanced resolution, which is close to the theoretical limit and beyond the Abbe diffraction limit.
We demonstrate that to form a high-intensity THz terajet (field localization) within the graphene monolayer placed at the shadow surface of one wavelength-dimensions dielectric particle with refractive index near 2 the cubic shape is preferable in comparison with spherical one. A spherical particle is more magnetic than electric due to multipole mode distributions. A graphene monolayer was applied for a picosecond timescale modulation of THz wave by controlling of IR radiation for integrated ultrafast all-optical THz modulator. Application of biological objects to the shadow surface of the mesoparticle instead of graphene will allow studying the biophysical aspects of the interaction of the electromagnetic field with such biological objects.
Based on the developed electro-optical cell detection system using dielectrophoresis, both the electrical and viscoelastic behavior of erythrocytes was studied. Studies were conducted to assess the possibility of using hemorheological parameters as precursors of stroke recurrence. As a result, the main hemorheological parameters of erythrocytes, such as electrical and viscoelastic properties, hemostasis indices, were determined. It is shown that these parameters can serve as harbingers of a relapse of a stroke.
We have developed a method of the terahertz (THz) solid immersion microscopy for the reflection-mode imaging of soft biological tissues. It relies on the use of the solid immersion lens (SIL), which employs the electromagnetic wave focusing into the evanescent-field volume (i.e. at a small distance behind the medium possessing high refractive index) and yields reduction in the dimensions of the THz beam caustic. We have assembled an experimental setup using a backward-wave oscillator, as a source of the continuous-wave THz radiation featuring λ= 500 μm, a Golay cell, as a detector of the THz wave intensity, and a THz SIL comprised of a wide-aperture aspherical singlet, a truncated sphere and a thin scanning windows. The truncated sphere and the scanning window are made of high-resistivity float-zone silicon and form a unitary optical element mounted in front of the object plane for the resolution enhancement. The truncated sphere is rigidly fixed, while the scanning window moves in lateral directions, allowing for handling and visualizing the soft tissues. We have applied the experimental setup for imaging of a razor blade to demonstrate the advanced 0:2λ resolution of the proposed imaging arrangement. Finally, we have performed imaging of sub-wavelength-scale tissue spheroids to highlight potential of the THz solid immersion microscopy in biology and medicine.
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