Unusual optical phenomena inside and near a rotating sphere: the photonic hook and resonance.

Based on the optical Magnus effect, the analytical expressions of the electromagnetic field that a spinning dielectric sphere illuminated by polarized plane waves are derived according to the "instantaneous rest-frame" hypothesis and Minkowski's theory. More attention is paid to the near field. The unusual optical phenomena in mesoscale spheres without material and illumination wave asymmetry that are the photonic hook (PH) and whispering gallery mode (WGM)-like resonance caused by rotation are explored. The impact of resonance scattering on PHs is further analyzed under this framework. The influence of non-reciprocal rotating dimensionless parameter γ on PH and resonance is emphasized. The results in this paper have extensive application prospects in mesotronics, particle manipulation, resonator design, mechatronics, and planetary exploration.

Scattering of a radially polarized Bessel beam by a PEMC sphere: photonic nanojet and bottle beam formation.

The scattering of a radially polarized (r p) Bessel vortex and nonvortex beam by a perfect electromagnetic conductor (PEMC) sphere is studied based on the generalized Lorenz-Mie theory. The electric and magnetic fields of the incident arbitrary-shaped polarized beams are constructed using vector spherical wave functions (VSWFs) and beam shape coefficients. The analytical expression of the scattered field is expanded using VSWFs and scattering coefficients, which are derived by considering PEMC boundary conditions. The expression of the normalized dimensionless far-field scattering intensity (NDFSI) is also defined and derived. The photonic nanojet (PNJ) and the "bottle beam" generated by the interaction between the PEMC sphere and the vortex and nonvortex Bessel beam under r p are emphasized in this paper. Moreover, the intensity and directivity of NDFSI are also considered. It has been found that the generation of the PNJ and the "bottle beam" is determined by the half-cone angle α 0 of the r p Bessel beam and admittance parameter M of the PEMC sphere. Furthermore, the influence of M, α 0, and integer order l of the Bessel beam on the intensity and distribution of NDFSI is also discussed. The findings are important in the research on meta-materials and promising prospects in microwave engineering, antenna engineering, imaging, subwavelength focusing, optical radiation force, and torque.

Curved photonic nanojet generated by a rotating cylinder.

The curved photonic nanojet (CPNJ) produced due to the interaction between a dielectric circular cylinder rotating at a stable angular velocity and a plane wave is investigated. Based on this model, the optical Magnus effect of a dielectric circular cylinder is verified. And the analytical expression of both internal and external electric field are given based on the instantaneous rest-frame theory and the partial-wave series expansion method in cylindrical coordinates. The influence of the size parameter, the relative refractive index, and the rotating dimensionless parameter on the CPNJ are analyzed and discussed in numerical results. The "photonic nanojet curved" effect is highlighted, which can be used to generate the off-axis photonic nanojet (PNJ) controlling particles by adjusting the angular velocity of the dielectric cylinder. The results of this manuscript have promising application prospects in optical tweezers, particle manipulation, and optical trapping. Moreover, it also provides theoretical support for the particle spinning and generation of the off-axis CPNJ.

Forecasting the atmospheric refractive index structure constant profile with an altitude-time correlations-inspired deep learning model.

An accurate forecast of the atmospheric refractive index structure constant (C n2) is vital to analyzing the influence of atmospheric turbulence on laser transmission in advance. In this paper, we propose a novel method to forecast the atmospheric refractive index structure constant C n2 profile, which is inspired by the turbulence characteristics (i.e., the altitude-time correlations). A deep convolutional neural network (DCNN) is adopted in the hope that with the stacked convolutional layers to abstract the altitude-time correlations of C n2, it can accurately forecast the C n2 profile in the near future based on the accumulated historical measurement data. While the sliding window algorithm is introduced to segment the measured time series data of the C n2 profiles to generate the input-output pair data for training and testing. Experimental results demonstrate its high forecast accuracy, as the obtained root mean square error and the correlation coefficient are 0.515 and 0.956 in the one-step-ahead C n2 profile forecast case, 0.753 and 0.9046 in the 36-step-ahead forecast case, respectively. Moreover, the forecast accuracy versus altitude and its relationship with the distribution of C n2 against altitude are analyzed. Most importantly, with a series of experiments of various input feature sizes, the appropriate sliding window width for C n2 forecast is explored, and the short-term correlation of C n2 is also verified.

Optical radiation force on a dielectric sphere by a polarized Airy beam.

The optical radiation force acting on a homogeneous and lossless dielectric spherical particle by a polarized Airy beam is analyzed in terms of the generalized Lorenz-Mie theory. The transverse and longitudinal radiation force components are theoretically evaluated and numerically simulated, emphasizing the transverse scale ω0, attenuation parameter γ, and polarization of the incident Airy beam versus the size parameter ka of the sphere. These results reveal that a polarized Airy beam can trap the dielectric sphere in its main caustic or sidelobes of the beam by the optical transverse force and be guided along the parabolic trajectory of the longitudinal optical force. Moreover, γ and ω0 of the Airy beams and ka of the dielectric sphere can affect the amplitude and distribution of the optical force components. This research may be helpful for the development of Airy optical tweezers in applications involving particle manipulation, optical levitation, particle sorting, and other emergent areas.

Optical Force on a Metal Nanorod Exerted by a Photonic Jet.

In this article, we study the optical force exerted on nanorods. In recent years, the capture of micro-nanoparticles has been a frontier topic in optics. A Photonic Jet (PJ) is an emerging subwavelength beam with excellent application prospects. This paper studies the optical force exerted by photonic jets generated by a plane wave illuminating a Generalized Luneburg Lens (GLLs) on nanorods. In the framework of the dipole approximation, the optical force on the nanorods is studied. The electric field of the photonic jet is calculated by the open-source software package DDSCAT developed based on the Discrete Dipole Approximation (DDA). In this paper, the effects of the nanorods' orientation and dielectric constant on the transverse force Fx and longitudinal force Fy are analyzed. Numerical results show that the maximum value of the positive force and the negative force are equal and appear alternately at the position of the photonic jet. Therefore, to capture anisotropic nanoscale-geometries (nanorods), it is necessary to adjust the position of GLLs continuously. It is worth emphasizing that manipulations with nanorods will make it possible to create new materials at the nanoscale.