各向异性的非相干矢量光束的传播特性

利用坡印亭矢量,研究了相干性为各向异性的非相干矢量光束在自由空间的传输特性,得到了光束横截面上能量分布及演化,导出了角偏振光束中心出现能量峰值的条件,详细分析了相干性对偶极子光束能量旁瓣的影响,并发现各向异性的偶极子光束具有三种不同的演化形式,得到了具体判据.     

矢量非傍轴厄米-拉盖尔-高斯光束的光束质量

基于矢量Rayleigh-Sommerfeld衍射积分，推导出矢量非傍轴圆偏振厄米-拉盖尔-高斯(HLG)光束的远场解析表达式.矢量非傍轴圆偏振高斯光束可作为一般公式的特例给出.将桶中功率(PIB)概念推广到非傍轴范畴，用以描述矢量非傍轴光束的远场光束质量，其中光强用时间平均坡印廷矢量的z分量取代.数值计算和分析表明，矢量非傍轴HLG光束的PIB不仅与束腰宽度与波长之比w₀/λ有关，而且还与α参数，模指数n和m以及所取桶的尺寸有关. 关键词： 矢量非傍轴厄米-拉盖尔-高斯光束 矢量Rayleigh-Sommerfeld衍射积分 桶中功率     

Angular momentum of gaussian light beams

Analysis of the orbital angular momentum of paraxial light beams shows that a key role in the formation of this quantity is played by phase relations between longitudinal and transverse radiation fields. When a light beam is circularly polarized or has a helical wave front, the azimuthal component of the Poynting vector and the density of orbital angular momentum prove to be non-zero. In the case of circularly polarized radiation, the azimuthal component of the Poynting vector and the density of the orbital angular momentum can change the sign at different points in the cross section of the light beam, while the total orbital momentum of the beam remains quantized.     

Propagation properties of chirped Airy vortex beams with x-polarization through uniaxial crystals

The propagation dynamics of a chirped Airy vortex(CAiV) beam with x-polarization in uniaxial crystals orthogonal to the optical axis is studied analytically and numerically. The effect of the ratio of extraordinary and ordinary refractive indices, the chirp parameter, as well as the propagation distance is analyzed, which shows that the focused position of the CAi V beams can be controlled through changing the ratio of the extraordinary and ordinary refractive indices. In addition,with the propagation distance increasing, the asymmetry of the intensity and the angular momentum of the CAi V beam during propagation becomes much more visible. The variation of the chirp parameters can change the attenuation velocity of the vortex as well.     

Double pulse quasi-collinear high harmonic generation scheme as a tool for X-ray laser plasma gain probing

We calculate the field distribution based on the vector diffraction theory for a superposition of spirally phase shifted radially polarized beams. Twisted longitudinally polarized field is found in the focal region. The total intensity as well as the polarization components rotates around the beam axis near the focus. Calculation of the Poynting vector at the focal plane shows that the electromagnetic energy is redistributed between different polarization components. Nonzero value of transverse components of the Poynting vector implies the transverse flow of the energy in the focal region.     

Spin-dependent transverse force on a vortex light beam in an inhomogeneous medium

Spin-dependent effects on vortex light beams propagating in an inhomogeneous medium are demonstrated by solving the full three-component field Maxwell equations using the perturbation analysis. It is found that the hybrid Laguerre–Gauss modes with polarization-orbital angular momentum (OAM) entanglement are the vector solutions of the Maxwell equations in a graded-index medium. Focusing of linearly and circularly polarized vortex light beams in a cylindrical graded-index medium is investigated. It is shown that the vortex light beam undergoes an additional transverse force acting differently on circular polarized beams with opposite handedness. The wave shape variation with distance taking into account the spin–orbit and nonparaxial effects is analyzed. Effect of long-term periodical revival of wave packets due to mode interference in a graded-index cylindrical optical waveguide is demonstrated.     

Evolution of Airy beams in a chiral medium

We study the evolution of Airy beams in chiral media. We numerically demonstrate that the circularly polarized Airy beams of opposite handedness can be separated when traveling through the chiral media. The constructive interference of the Airy beams in the near- and far-zone is explicitly analyzed by varying the chirality parameter of the medium. It is interesting to find that the self-acceleration of the beam is sensitive to the interference term.     

Rotating vectorial vortices produced by space-variant subwavelength gratings

A new class of vectorial vortex based on coherent addition of two orthogonal circularly polarized Bessel beams of identical order but with different propagation constants is presented. The transversely space-variant axially symmetric polarization distributions of these vectorial fields rotate as they propagate, while they maintain a propagation-invariant Bessel intensity distribution. These properties were demonstrated by use of discrete space-variant subwavelength gratings for 10.6 microm CO2 laser radiation. The polarization properties were verified by both full space-variant polarization analysis and measurements. Rotating intensity patterns are also demonstrated by transmitting the vectorial vortices through a linear polarizer.     

Tight focusing of linearly and circularly polarized vortex beams; effect of third-order spherical aberration

Tight focusing of linearly and circularly polarized vortex beams is studied in the presence of third-order spherical aberration, using vectorial Debye–Wolf integral. Results for total intensity distribution are presented for both polarizations. In addition, results for x-, y-, and z-polarization components are presented for the circularly polarized beam. Generation of longitudinal optical vortex in the tightly focused left circularly polarized beam has also been demonstrated by plotting its phase distribution. Compensation for the effect of spherical aberration has been studied in the presence of defocusing. Effect of aberration on the dark core of a tightly focused azimuthally polarized beam is also investigated.     

Multiple filamentation of circularly polarized beams

We derive a new system of equations that describes the propagation of circularly polarized laser beams in a Kerr medium. Analysis and simulations of this system show that multiple filamentation is suppressed for circularly polarized beams.     

Structure of a tightly focused vortex beam in the presence of primary coma

Structure of a tightly focused circularly polarized vortex beam in the presence of primary coma has been studied by using Debye-Wolf diffraction integral. The role of topological charge and handedness of the polarization on the focused structure has been discussed. Results have been presented for the total intensity and squares of the polarization components for left-, and right circularly polarized vortex beams. Impact of coma, on the dark core of an azimuthally polarized non-vortex beam is also investigated and compared with the dark core of a circularly polarized vortex beam. The presence of comatic aberration in the focusing system results in a positional shift of the high intensity lobes, and reduction of the intensity on one side of the center. Effect of coma on the focused structure has also been discussed in the context of STED microscopy.     

Reversal of the dipole vortex in a negative index of refraction material

When a small particle is illuminated by a circularly polarized laser beam, the induced electric dipole moment rotates in a plane. The flow lines of the emitted electromagnetic energy are the field lines of the Poynting vector. When the particle is embedded in a dielectric, these field lines have a vortex structure, and the rotation in the vortex has the same orientation as the rotation direction of the dipole. We show that when the embedding medium is a negative index of refraction material, the direction of rotation in the vortex is reversed.     

Dressed Airy Vortex Beam in a Hot Atomic Medium

Introducing vortices into an Airy beam by the interference between the lobes of the Airy beam for the first time, the modulation of Airy vortices is experimentally and theoretically investigated by electromagnetically induced transparency (EIT) effect and changing the number of side lobes of the Airy beam. The formation and disappearance of vortices in Airy beams can be caused by changing the number of side lobes. The EIT effect can induce the movement of vortex phase singularity by regulating the intensities of lobes in Airy beams. However, changing the number of side lobes can change the energy distribution of the lobes through the energy flow due to the self-healing of Airy beams, thus causing the displacement of vortex phase singularity. In addition, the simulation of the Poynting vector shows that the less the side lobes are blocked, the more energy can be retained in the main lobe and the unblocked side lobes, so that the overall shape of the Airy beam can be better maintained. Such studies provide a new method to acquire and adjust Airy vortex beams and can be applied in the realm of optical micromanipulation.     

Propagation properties of the chirped Airy vortex beams through left-handed and right-handed material slabs

We present an investigation on the propagation properties of the chirped Airy vortex(CAi V) beams through slabs of left-handed materials(LHMs) and right-handed materials(RHMs). We discuss the influence of chirped parameter C on the propagation of the CAi V beams through LHM and RHM slabs. Our simulation results show that a maximum accelerated velocity appears during the propagation process. The intensity concentration of the CAi V beams increases with the absolute value of the chirped parameter. The peak intensity of the CAi V beams changes abruptly, and the chirped parameter plays an active role on the difference of the maximum and the minimum. In the energy flow, we find that the effects of the chirped parameter on the strength of the vortex are different at different propagation distances.     

Multiple scattering of polarized light in a turbid medium

It is shown that multiple scattering of polarized light in a turbid medium can be represented as independent propagation of three basic modes: intensity and linearly and circularly polarized modes. Weak interaction between the basic modes can be described by perturbation theory and gives rise to “overtones” (additional polarization modes). Transport equations for the basic and additional modes are derived from a vector radiative transfer equation. Analytical solutions to these equations are found in the practically important cases of diffusive light propagation and small-angle multiple scattering. The results obtained are in good agreement with experimental and numerical results and provide an explanation for the experimentally observed difference in depolarization between linearly and circularly polarized waves.     

Properties of circularly polarized vortex beams

The properties of circularly polarized vortex beams in cylindrical polarization bases are studied. A circularly polarized vortex beam is decomposed into radial and azimuthal polarization. With the proper combination of vortex charge and the handedness of the circular polarization, a focal field with an extremely strong longitudinal component as well as a flat-topped profile can be obtained. The cylindrical decomposition also sheds light on the connections between orbital angular momentum and the spin of the light beams.     

Free-space propagation of autofocusing Airy vortex beams with controllable intensity gradients

Vortex splitting is one of the main causes of instability in orbital angular momentum(OAM) modes transmission. Recent advances in OAM modes free-space propagation have demonstrated that abruptly autofocusing Airy vortex beams(AAVBs) can potentially mitigate the vortex splitting effect. However, different modes of vortex embedding will affect the intensity gradients of the background beams, leading to changes in the propagation characteristics of vortex beams. This study presents the unification of two common methods of coupling autofocusing Airy beams with vortices by introducing a parameter(m), which also controls the intensity gradients and focusing properties of the AAVBs. We demonstrate that vortex splitting can be effectively reduced by selecting an appropriate value of the parameter(m) according to different turbulence conditions. In this manner,the performance of OAM-based free-space optical systems can be improved.     

Scattering forces and electromagnetic momentum density in crossed circularly polarized standing waves

We analyze the forces on a small dipolar particle and the electromagnetic momentum density in a configuration consisting in two perpendicular circularly polarized stationary waves. The field distribution shows regions in which the electric and magnetic fields are parallel corresponding to a null Poynting vector. Although the average value of the momentum density, proportional to the Poynting vector, is zero in these regions, there are scattering forces acting on small particles due to light's spin force. The total scattering force suggests a new definition of the average value of the momentum density for free propagating electromagnetic fields.     

Propagation dynamics and experimental observation of quadratic vortex beam

The concept of a quadratic vortex beam is proposed, in which phase term of the beam is given by exp(i mθ²). The phase of the quadratic vortex beam increases with azimuthal angle nonlinearly. This change in phase produces several unexpected effects. Unlike the circularly symmetric beam spot of normal vortex beams, the intensity distribution of the quadratic vortex beam is shown to be asymmetric. The phase singularities will shift in the transverse beam plane on propagation.     

Twist defect in chiral photonic structures

We demonstrate that twisting one part of a chiral photonic structure about its helical axis produces a single circularly polarized localized mode that gives rise to an anomalous crossover in propagation. Up to a crossover thickness, this defect results in a peak in transmission and exponential scaling of the linewidth for a circularly polarized wave with the same handedness as structure. Above the crossover, however, the linewidth saturates and the defect mode can be excited only by the oppositely polarized wave, resulting in a peak in reflection instead of transmission.