Magnetoplasmons in gapped graphene in a periodically modulated magnetic field

Motivated by recent experiments on long‐lived magnetoplasmons in the presence of a perpendicular magnetic field, we investigate the dynamical dielectric response function of graphene in contact with a substrate using the random phase approximation. We add a periodically modulated magnetic field within the graphene plane and address both the inter and intra Landau band magnetoplasmons. Verification of the predicted magnetic modulation effects is possible by experiments analogous to those for the zero gap limit.     

High-frequency asymptotic expansions of a backscattering cross-section and an HH/VV polarization ratio for smooth two-dimensional surfaces

High-frequency asymptotic expansions of electrical and magnetic fields are obtained at a perfectly conducting smooth 2D surface illuminated by a plane incident wave in two cases of TE and TM polarization. Corrections to the geometrical optics backscattering HH and VV cross-sections are derived and the polarization ratio HH/VV is estimated for the specular points of a general form. It is shown that the coefficient of the first term in this series ∼ 1/k² depends not only on the local surface curvature radius at the specular reflecting points,but also on higher derivatives up to the sixth order.

For backscattering from a statistically rough surface, averaging over surface random derivatives at the specular points was performed. It was shown that for statistically uniform (stationary on space variables) random surfaces, the polarization ratio HH/VV (dB) is positive on average and proportional to ∼ 1/k²     

Chiral optical Tamm states at the boundary of the medium with helical symmetry of the dielectric tensor

We report the observation of photovoltage oscillations in back-gated two-dimensional electron systems when tuning the density under incident microwaves and in the absence of a magnetic field. The oscillations are periodic in the inverse of the square root of the density. They originate from the interference of screened bulk plasmons with a linear dispersion. This phenomenon can be exploited to devise a spectrometer-on-a-chip for millimeter waves. The influence of a perpendicular magnetic field is investigated and reveals a transformation of screened bulk plasmons waves into screened edge magnetoplasmons.     

Surface magnetoplasmons in a structure with a two- and three-dimensional plasma

Collective oscillations of a two-component structure consisting of a plasma half-space with a two-dimensional plasma layer at its boundary in the presence of a magnetic field have been studied. Possible variants of the spectra of surface magnetoplasmons have been analyzed for three main mutual orientations of the magnetic field, wavevector, and normal to the surface. The case of the field parallel to the boundary where the frequency is an odd function of the wavevector has been discussed in detail.     

Occurrence of a gap in the spectrum of magnetoplasma excitations of a two-dimensional electron disk subjected to a strong in-plane magnetic field

The effect of a parallel magnetic field on the dispersion of bulk and edge magnetoplasmons in a disk-shaped two-dimensional electron system is investigated. It is found that the anisotropy of the electron effective mass that appears in a parallel magnetic field lifts the degeneracy of plasma oscillations in the disk. This is accompanied by the occurrence of a gap in the spectrum of magnetoplasmons, and the magnetic dispersion of these excitations changes from a linear to a parabolic one. The width of the gap is determined by the difference between the frequencies of plasma oscillations along the field and transverse to the field and grows quadratically with the in-plane field strength.     

Fast iterative approach to the difference scattering from a dielectric target above a rough surface

The difference field RCS (d-RCS) has been defined to analyze the scattering from the target above a rough surface. The electric field integral equations (EFIEs) of the difference induced currentJ _sd on the rough surface, the induced electric currentJ _o and magnetic currentK _o on the dielectric target under a TE wave incidence are derived. A small portion of the rough surface towards the target along the specular direction is taken to compute the scattering contributionE _s0 from the rough surface towards the target, which improves the computation speed. A numerical iterative approach is developed to solve the EFIEs and bistatic d-RCS. The surface length for iterations is dependent on the scattering angle and discussed for comparison with Johnson’s method. Using the Monte-Carlo method to generate the Pierson-Morkowitz (P-M) ocean-like rough surface, bistatic d-RCS of the dielectric target, e.g. a cylinder or a square column, above the rough surface is numerically simulated. The induced electric and magnetic currents on the dielectric target and the difference induced current on the rough surface are numerically discussed.     

Fast iterative approach to the difference scattering from a dielectric target above a rough surface

1 Introduction Electromagnetic scattering from the target above or beneath a rough surface has at- tracted much interest during recent years, because of extensive applications to radar surveillance, target detection, ground radar probing, and so on[1―3]. In order to numeri- cally simulate scattering from composite model of the target and underlying rough sur- face, some fast numerical methods, such as general forward backward method and spec- trum acceleration algorithm (GFBM/SAA)[4,5], fin…     

A new approach for noninvasive skin blood imaging in microcirculation

A new noninvasive method is proposed for optically imaging blood under skin. A mini-mirror is used to guide the light incident onto the skin surface, while blocking specularly reflected light from the tissue. Moreover, by using two linear polarizers at right angles, the specular reflection can be reduced further, while also blocking the rough surface scattered light. A circular polarizer may be used to obtain the same effect. As a result, the blood flow beneath the surface of skin can be visualized clearly. The effect of the mini-mirror is also analyzed theoretically and experimentally.     

微粗糙硬铝表面双向反射特性实验研究

本文基于四波段双向反射分布函数测试平台,对微粗糙硬铝表面的光谱双向反射分布函数进行了实验测量,考察了微粗糙尺寸参数、入射角度和入射辐射波长对表面辐射特性的影响。测量结果显示了明显的镜反射特征,粗糙的表面结构还引起了后向反射增强现象,长波入射和大角度入射增强后向反射效应。     

Magnetic field effects on the optical properties of an azo-dye doped liquid crystal

Homeotropically aligned nematic liquid crystals doped with azo-dye were subjected both to a linear polarized light of a He–Ne laser and to a magnetic field perpendicular to the incident light beam. We found that the emerging light was elliptically polarized when using magnetic field strengths higher than the threshold value for the magnetic Freedericksz transition. The light transmission, the rotatory power (induced by azo-dye) and the ellipticity varied quasiperiodically when increasing magnetic field strength. The number and positions of maxima and minima depend on the cell thicknesses. Changes in the phase difference between the emergent ordinary and extraordinary rays were computed from the experimental data and the magnetic field dependence of the birefringence was determined.     

Measurement of the mean free path of edge magnetoplasmons revealed in the spectra of magnetic oscillations of photovoltage in a two-dimensional electron system under microwave radiation

In the spectrum of photovoltage oscillations that are periodic with respect to the magnetic field and appear on Hall structures under microwave irradiation, two frequency components of oscillations are observed and analyzed. The appearance of these two frequencies in photovoltage oscillations is explained by the existence of two trajectories of edge magnetoplasmons and by the effects of the interference of collective excitations on these trajectories. The effects of the temperature, microwave radiation frequency, and magnetic field strength on the mean free path of edge magnetoplasmons are analyzed.     

Synthetic spectra from rough-surface scattering

We present a method for designing a one-dimensional, deterministic, perfectly conducting rough surface that scatters light at a fixed scattering angle with an intensity whose dependence on the frequency of a plane wave incident normally upon it reproduces the infrared spectrum of a known substance within a specified region of frequencies. Such a surface can therefore be used in a correlation spectrometer for the identification of unknown substances.     

The linear dispersion coefficient of surface magnetoplasmons

The dispersion of surface magnetoplasmons supported on a semiconductor-vacuum interface which is normal to an applied magnetic field is investigated. It is assumed that the surface possesses a depletion layer and that the dispersion is of hydrodynamic origin. Dimensionless numerical results are obtained for the magnetic field dependence of the linear dispersion coefficient with special reference being given to n-type InSb.     

Height distribution on a rough plane and specularly diffracted light amplitude are Fourier transform pair

In this report we show that the amplitude of specularly diffracted light from a plane rough surface as a function of incident angle cosine is Fourier transform of the height distribution on the surface. Therefore, an even height distribution function, which is the case for many rough surfaces, can be obtained by measuring the specularly diffracted light intensities. Also, it is observed that for polychromatic illumination the spectrum of the specularly diffracted light is modified and the modification depends on roughness, incident angle, and wavelength. It is also shown that, for a fixed incident angle, the height distribution on the rough plane is Fourier transform of the spectral modifying function. Experimental studies on some surfaces of different roughnesses, prepared by grinding sheet-glasses by powders of different grain sizes, show that the corresponding height distributions are Gaussian and the rms heights obtained by the two approaches are quite consistent.     

Discrete dipole approximation simulations of light reflection from flat non-transparent particles with rough surfaces

We study light reflection from flat particles with rough surfaces and fractal statistics of topography. Discrete dipole approximation method is used to solve the problem of light scattering. Refractive indices corresponding to a metal and a transient material with conductive properties are taken. The sizes of particles are much larger than the wavelength of incident light and the roughness scales are larger, comparable to and smaller than the wavelength. The influence of the fractal dimension parameter and the amplitude of heights of random topography on reflectance and on the angular profile of the specular reflection peak is considered. Our calculations demonstrate that topography amplitude is very important for reflectance and fractal dimension is responsible for the angular dispersion of the specular reflection peak.     

Interaction of surface magnetoplasmons and surface optical phonons in polar semiconductors

A theoretical investigation has been carried out of surface polaritons associated with surface magnetoplasmons coupled to surface optical phonons in polar semiconductors. The coupled mode frequencies are calculated for several orientations of the magnetic field relative to the surface and the direction of propagation in the large wave vector (unretarded) limit. Dispersion curves are calculated for the configuration in which the magnetic field is parallel to the surface and is perpendicular to the wave vector. Experimental possibilities for observing the interaction effects are discussed.     

Dynamic generation of beating signals in an atomic system with a static magnetic field

In an \(F_{e}=0\,\leftrightarrow \,F_{g}=1\) transition, which interacting with a weak \(\pi \) -polarized probe field and a strong \(\sigma \) -polarized coupling field, we obtain the controlled beating signals depending on the applied magnetic field. In this configuration, we devise a procedure of light storage and retrieval where the magnetic field is switched off in the storage stage, but the magnetic field is switched on in the retrieval stage. Therefore, the beating signals is generated in the retrieval stage, which exhibits a series of maxima and minima in intensity. In addition, we can obtain two fast optical precursors and slow beating singals when the incident probe field is a squared pulse.     

On the theory of X-ray coherent reflection from a rough surface

A solution of the problem of X-ray specular reflection from a statistically rough surface is presented. It is based on using the Green function formalism. The Kirchhoff formula is used to describe the transmission of the wave field through a rough interface. Generally, microscopically exact expressions for the coefficients of transmission through a rough surface and reflection from it are obtained by taking multiple scattering effects into account. Averaging of the obtained expressions over possible realizations of random roughness of the interface between media allows to obtain rigorous expressions for specular reflection and transmission coefficients. The behavior of exact solutions in the limiting case of infinite correlation lengths is studied. It is shown that, in this case, the obtained solution corresponds to the Debye-Waller normalization. Expressions for the reflection and transmission coefficients making it possible to carry out numerical calculations are obtained in the Bourret approximation of multiple-scattering theory.