The photonic hook (PH) generated by a partially illuminated high-index dielectric particle hemi-immersed in the dielectric film is investigated. A tunable PH is generated from a cylinder deposited on a dielectric film, and the cylinder is partially illuminated by the placement of a thin, flat aluminum mask in front of it. The effects of film type, mask width, and height of dielectric film are mainly discussed. The results provide a novel design method for PHs, which have potential applications in optical manipulation and high-resolution imaging.
Water droplets are a highly abundant phase-change material to realize tunable optical lenses. We demonstrated for the first time that freezing mesoscale water droplets could be used as a tunable optical lens, such that freezing becomes an asset despite the low absolute values of the refractive indices of the shell and core materials and their optical contrast. It is shown that the dielectric shell of mesoscale water droplets in solid ice allows controlling both the maximum field intensity and the focus position of the formed photonic nanojet. The ice formation with air bubbles during the freezing of a water droplet is appropriate for a dynamic increase in the range of change of the focal position compared to solid ice. The proposed concept of a tunable spherical lens based on a freezing water drop can be used for microscopy and optical trapping in "green" mesotronics.
The scattering of polarized plane waves on a rotating spherical particle, especially the far-field characteristics, is studied based on the “instantaneous rest-frame” hypothesis and Minkowski’s theory. The influence of the rotating angular velocity on the scattering is emphasized and is expressed as the dimensionless parameter y. The effects of incident light polarization states and particle size parameter ka are investigated on this basis. Besides, the loss of particles is also introduced. Besides, the influence of material on the scattering characteristic of rotating particles is also a concern, and the particle loss is introduced. Related results have promising applications in the material property research and target detection fields. Furthermore, they can also be extended to planetary research and detection, which plays a vital role in exploring the mysteries of the universe.
The red blood cells, the role of which is difficult to underestimate in life and biology, were usually chosen as a sample for observation in an optical microscope. In this paper, we show that using optical microscopy based on high-index spherical mesoscale particles with a refractive index of 1.9, generating a non-evanescent curved light beam with subwavelength structures – so-called a structure light photonic hook by partial illumination conditions, it is possible to study the transformation dynamics of an erythrocyte into an echinocyte. Examples of images are presented. The findings in this manuscript have promising application prospects in nanomanipulation, biology, and medicine.
This paper studies the photonic hooks (PH) generated by the interaction of a dielectric sphere rotating at a certain angular velocity with a plane wave. Based on the instantaneous static frame theory and the partial-wave series expansion method in spherical coordinates, with the help of the separated variable method, we obtain the analytical solutions for the internal and external electric fields of a homogeneous isotropic dielectric sphere rotating around the z-axis irradiated by a plane wave of arbitrary direction. This article focuses on the effect of size parameters (ka), relative refractive index (m1), and rotational dimensionless parameters 𝛾 on PH. The PH produced by this non-reciprocal system can be used not only for trapping off-axis particles, but also has promising applications in low-loss waveguiding, subdiffraction-resolution nanopatterning, and nanolithography.
Based on the optical Magnus effect, the theoretical framework that scattering generated by a plane wave illuminating a spinning dielectric sphere is proposed using the “instantaneous rest-frame” hypothesis and Minkowski's theory. The analytic expressions of electromagnetic fields are derived for a dielectric sphere rotating around the z-axis exerted by a plane wave illuminating in an arbitrary direction using the method of separation of variables. Both the photonic hook (PH) and the resonance scattering generated by the spinning dielectric sphere are concerned and investigated. The impact of resonance scattering generated by the rotation on the PH is also discussed. The influence of the non-reciprocal rotating dimensionless parameter which determines the existence of PH and resonance to the scattering is emphasized. All the findings in this manuscript have extensive application prospects in particle manipulation, designing of the resonator, and mesotronics.
The resonance scattering caused by the interaction between a dielectric cylinder rotating at a steady angular velocity and a plane wave are studied using the method of separation of variables and the multipole expansion method. In addition, the effect of resonance on curved photonic nanojets (PNJ) is also analyzed. During the study, the critical value of resonance scattering is found by changing the dimensionless and dimensional parameters of the medium cylinder. It is found that the rotation of particles can create and destroy resonance phenomena. The resonance scattering of rotating dielectric cylinders produced by plane waves provides a new direction for the study of PNJ and whispering gallery mode (WGM), as well as the design and application of ultra-sensitive sensors and resonators
With the rapid development of computational electromagnetics and information science, electromagnetic inverse scattering has attracted more and more attention, and has become one of the most active and cutting-edge research topics in the field of electromagnetics. Traditional inverse scattering schemes are computationally slow, and machine learning has emerged as a relatively new and efficient inverse scattering solution in recent years. This article will build a fully connected neural network for the inverse scattering of a charged sphere illuminated by a plane wave. Parameters such as the charge and radius of spherical particles are used as the input of the neural network. The corresponding far-field scattering intensities are derived by the generalized Lorenz-Mie theory (GLMT). The numerical results of the field intensity corresponding to different scattering angles are sampled as the output of the neural network. Through network parameter adjustment, a forward model is obtained by training. Then take the far-field intensity sampling point as the label as the input to randomly initialize the particle parameters, and realize the inversion of the particle parameters through the stochastic gradient descent algorithm. Compared with the actual value, the relative error is less than 2%, which realizes high-precision real-time inversion of charged spherical particles. This research has important application value in measuring the scattering properties (such as charge, size, etc.) of particles.
To study the joint effects of turbulence and fog on free-space optical (FSO) communication, a joint fog-turbulence-pointing error probability model for FSO is derived based on the random fog channel, Malaga turbulence model, and pointing error model. The closed-form expressions for the average signal to noise ratio (SNR), outage probability, average bit error rate (BER), ergodic channel capacity, and moment generating function in FSO communication under intensity modulation/direct detection are derived based on the joint model. Based on the unmanned aerial vehicle (UAV) working scenario, applying these expressions, the performance analysis of the inter-UAVs optical wave communication is implemented under the conditions for different beam widths, turbulence intensity and fog density and the pointing error caused by position, orientation, and jitter deviations. The calculated results are in good agreement with the Monte Carlo simulations. The analytical results for the average BER and outage probability show that the increase in beam width can significantly degrade the BER and outage probability, for the UAVs optical communication link. The analysis for the ergodic channel capacity shows that it increases with the increase of average transmission power; however, it increases slowly with the increase of beam width. And the increase in turbulence intensity, fog density, and drone jitter will degrade the communication performance of the system. Our study lays an important theoretical foundation for the development of FSO communication and UAV communication performance improvement in joint fog and turbulent environment.
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.
The optical spin torque (OST) on a magneto-dielectric Mie sphere has been discussed and analyzed analytically in this investigation, using the Generalized Lorenz-Mie theory (GLMT). The incident electromagnetic field is an Airy light-sheet, with the parameters transverse scale kω0 and attenuation parameter γ, where kω0 modulates the width of the main lobe of the Airy light-sheet, and γ controls the attenuation of Airy light-sheet. The effect of kω0 and γ of Airy light-sheet on the OST has been studied. The size parameters ka, permittivity, and permeability of the magneto-dielectric Mie sphere have also been discussed. This investigation of the optical spin torque (OST) on the magneto-dielectric Mie sphere has specific reference significance and is expected to be applicable to the field of manipulation of microparticles and biomedicine.
As the tweezer light sources, single beam optical traps, have become a kind of important tool for non-contact manipulation of microscopic objects. The interaction of light-sheets with objects allows flow visualization, nondestructive optical sectioning and imaging of the internal subcellular features. In the framework of GLMT, based on the vector angular spectrum decomposition method, with the Lorenz gauge condition and Maxwell’s equations allow adequate determination of the Cartesian components of the incident radiated electric field components. The Bessel pincer light-sheets with characteristics of auto-focusing and self-bending, has great advantages in non-destructive optical sectioning and imaging of the internal subcellular features. The influences of the Bessel pincer light-sheets (mainly focusing on beam order and scaling parameter) acting on a dielectric sphere particle, will be discussed. The results will show the sensitivity of beam parameters (beam order and scaling parameter) to the radiation force and the negative force. Further, the present solution can be used to calculate the optical torque, which is of great importance in particle transport and rotation.
Optical trapping is of great practical importance in various fields such as physics, biology and nanofluidics or
microfluidics. In order to trap and move particles efficiently, it is necessary to theoretically study the radiation pressure
face exerted on the particles firstly. We introduce Debye series expansion (DSE), which can give physical explanation of
each scattering process, to analyze radiation pressure force exerted on a spherical particle generated by focused beams.
The DSE is employed to the study of radiation pressure force corresponding to single scattering process, and to the
research on the effect of various parameters such as beam position and mode p on radiation pressure force.
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