Second-harmonic generation by intense beams containing phase dislocations:self-breaking into sets of solitons

Second-harmonic generation of light in bulk quadratic non-linear media with intense input beams containing phase dislocations is studied numerically under conditions for TypeI phase-matching. We investigate how, above a threshold light intensity, the input beams self-split along the azimuthal direction into a pattern of separate beams which then form a set of spatial solitons. The mechanism of such a behaviour is the azimuthal modulational instability of the ring-shaped, mutually trapped fundamental and second-harmonic beams containing the phase dislocations. This revised version was published online in November 2006 with corrections to the Cover Date.     

Rotation of multimodal Gauss–Laguerre light beams in free space and in a fiber

A gradient algorithm is proposed for design of phase diffractive optical elements (DOEs) that can form the light beams being effectively a superposition of a small number of nonradially symmetric Gauss–Laguerre modes with a preset energy contribution of each mode. We show that under certain conditions there is a rotation of the cross-section of such light beams. The rotation of multimodal Gauss–Laguerre light beams propagating in a fiber with quadratic dependence of the refractive index is discussed.     

Acoustooptical interaction of light beams under conditions of internal conical refraction

The collinear acoustooptical (AO) interaction of light beams under conditions of internal conical refraction is considered. The dependences of the diffraction efficiency on the ratio of radii of light and ultrasonic beams, the AO coupling length, and the ultrasound intensity are found. An analytical expression is obtained describing the diffraction efficiency of collinear AO conversion of annular beams of internal conical refraction.     

Interference comparative analysis of the shape of wavefronts of incoherent light beams

A technique of interference comparative analysis of the shape of wavefronts that can be applied to incoherent light beams is proposed. The difference in the shape of the wavefronts of the incoherent light beams under study is visualized by using the moire pattern appearing upon superposition in real time of the lateralshear interferograms or their photographs. The possibility of producing the interference pattern that visualizes the difference in the shape of the wavefronts of incoherent beams with an enhanced measurement sensitivity is shown. The results of experimental testing of this technique in visualization of the difference between the shapes of the wavefronts of two light beams emitted by different lasers are presented.     

Incoherent interaction of Gaussian beams in photorefractive optically active crystals

The incoherent interaction of (1+1)-dimensional Gaussian beams in cubic photorefractive optically active crystals is theoretically considered. The effect of optical activity on the interaction process is discussed. The obtained results are compared with those for the case of the coherent interaction. It is shown that during of the interaction between orthogonally polarized Gaussian beams one of them is deflected under the action of the other. This phenomenon is promising for the realization of optical address positioning of light beams. PACS 42.65.-k; 42.62.Jx; 42.70.Nq     

Specifics of electromagnetic TE waves splitting and combining under the conditions of frustrated total internal reflection in a thin dielectric layer

The possibility of designing optical beam splitters based on frustrated total internal reflection (FTIR) is considered. A theory describing splitting of a single light wave into two waves and interference of two light waves in a thin dielectric gap under the FTIR conditions is presented. The resulting expressions are analyzed, and the curves describing the behavior of light beams in the process of their splitting and combining in a thin dielectric layer under the FTIR conditions are plotted.     

高阶椭圆厄密–高斯光束的轨道角动量研究

从傍轴条件下光束轨道角动量的基本理论出发,根据高阶椭圆厄密–高斯光束的光场分布,运用张量方法,对高阶椭圆厄密-高斯光束轨道角动量的密度分布进行了理论分析,得到了求解该密度分布的计算公式,并在给定参量条件下作了数值模拟.进一步对光束中每个光子携带的平均轨道角动量进行了计算,发现其值随着椭圆厄密-高斯光束阶次的增大而增大,表明高阶椭圆厄密-高斯光束能够比椭圆高斯光束或拉盖尔-高斯光束提供高得多的轨道角动量.     

Generation of the Second Harmonic by Bessel Light Beams Under the Conditions of Quasisynchronism

The specific features of the doubling of Bessel light beams in quasisynchronous interaction in periodically polarized nonlinear crystals are investigated. A theoretical model has been developed, which is based on the representation of the second-harmonic field in the form of superposition of Bessel beams. Based on the analysis of overlapping integrals, two groups of modes responsible for the formation of the central and circular beams of the second harmonic under the conditions of quasisynchronism were distinguished. It is found that, unlike homogeneous media, crystals with periodic polarization can be used for doubling the frequency of Bessel beams with cone angles changing in wide limits.     

Array illuminator based on self-imaging in white light

An array illuminator is a device/optical system that splits an incoming beam of light into an array of many light spots/beams. It is useful in logic systems and in optical digital computing or in switching systems to energize arrays of components such as logic gates, optically bistable devices and electro-optic modulators. Array illuminators working in white light are interesting because they do not suffer from coherent noise and yield better signal-to-noise ratio. We propose configurations for array illuminator based on Fresnel diffraction and working under white light illumination conditions. Performance evaluation of the illuminators is also undertaken and the results of investigation are reported.     

Correction of nonlinear distortions of light beams by an optical system with feedback

The operation of a phase-conjugate COAT system under conditions of thermal self-interaction is investigated. The analogy between the phase conjugation and optimal focusing algorithms is discussed. A method is proposed for raising the stability of the adaptive system under conditions of strong nonlinearity. The possibility of using an optical system with feedback to suppress thermal spreading of light beams is analyzed on the basis of the results of a numerical simulation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 15–20, October, 1980.     

Energy exchange between four copropagating light waves under conditions of diagonal bipolar nonlinearity

Stationary energy exchange between four copropagating light beams in a medium with diagonal bipolar nonlinearity is studied. This type of nonlinearity is common in nematic liquid crystals. Solutions of underlying Hamilton’s equations are thoroughly analyzed with the phase-plane approach for different wave-vector mismatches. The existence of an unstable eigenmode is demonstrated geometrically. This mode results from the considerable difference between the temperature dependences of the ordinary and extraordinary refractive indexes. Exact analytic solutions related to various regions of the phase plane are presented. Optical switching is demonstrated to be feasible under the stated conditions. It is found that the energy exchange essentially depends on the input phase mismatch. Intensities required for observing the predicted effects are evaluated.     

The spectral combination characteristic of grating and the bi-grating diffraction imaging effect

This paper reports on a new property of grating, namely spectral combination, and on bi-grating diffraction imaging that is based on spectral combination. The spectral combination characteristic of a grating is the capability of combining multiple light beams of different wavelengths incident from specific angles into a single beam. The bi-grating diffraction imaging is the formation of the image of an object with two gratings: the first grating disperses the multi-color light beams from the object and the second combines the dispersed light beams to form the image. We gave the conditions necessary for obtaining the spectral combination. We also presented the equations that relate the two gratings’ spatial frequencies, diffraction orders and positions necessary for obtaining the bi-grating diffraction imaging.     

空心锥状双高斯光束传输特性研究

建立了空心锥状双高斯光束的模型.在空心高斯光束模型的基础上,由初始光场的光强分布,利用柱坐标下的柯林斯公式,导出了空心锥状双高斯光束经过傍轴光学系统的解析传输变换式由传输变换式计算分析了空心锥状双高斯光束在自由空问的可控传输特性,及在1,10和60 m的截面光环的光强分布.用KNbO3双轴晶体进行实验,获得了空心锥状双高斯光束,外锥折射的锥角等于入射光会聚角.实验表明,当空心光束处于锥状发射状态时,空心光束的光环内黑斑面积随传输距离的增加而增加,实验结果与模型吻合较好.该研究为进一步设计制备基于空心锥状舣高斯光束的新型激光元件提供了理论依据和设计参量.     

Scattering of atoms by light

This review discusses the latest theoretical and experimental achievements in the resonant light pressure acting on the translational motion of atoms. Alongside with the effects due to the spontaneous light pressure (atomic deflection, velocity bunching, cooling), various manifestations of the effects of induced light pressure are considered in detail. This paper provides the theory and experiments of atoms scattering by a standing light wave under the conditions of coherent and non-coherent interaction, diffraction and interference of atomic beams. The problems where atomic motion along two trajectories and Landau-Zener transitions between them are essential, are studied. The kinetic phenomena (scattering, cooling, channeling) due to the motion of the particles exposed to gradient force and also friction and diffusion caused by spontaneous emission are considered. The influence of the recoil effect under spontaneous emission of atoms on non-linear polarization phenomena is discussed.     

Nonparaxial propagation of phase-flipped Gaussian beams

This paper derives the closed-form expressions for nonparaxial phase flipped Gaussian （PFG） beams propagating in free space, through a knife edge and an aperture, which enable us to study nonparaxial propagation properties of PFG beams and to compare nonparaxial results with paraxial ones. It is found that the f parameter, offsetting distance of the knife edge and truncation parameter affect the nonparaxial beam propagation properties. Only under certain conditions the paraxial approximation is applicable. The results are illustrated by numerical examples.     

简单结构超表面实现波长和偏振态同时复用全息显示新方法

本文基于衍射光学设计理论,提出了仅用一种简单结构实现波长和偏振态同时复用全息显示新方法.构建了不同入射条件下超表面微元的结构参数与透过相位之间的映射关系,建立了科学的评价函数,优化得到超表面每个像素点处最优的单一结构超表面微元尺寸.仿真结果表明,本文设计的超表面实现了波长为532 nm的x线偏振光和波长为633 nm的y线偏振光入射显示不同形状字符的功能.     

Collinear Acousto–Optic Interaction of Light Beams near the Optical Axes of Biaxial Crystals

Collinear acousto–optic interaction of light beams near the optical axes of biaxial crystals, including gyrotropic ones, is considered. Efficient acousto–optic transformation of fast and slow light beams under the conditions of internal conical refraction has been revealed. It is shown that the width of the transmission band and the central frequency of ultrasound in collinear acousto–optic filtration in a nongyrotropic crystal are determined by the angle at the apex of the cone of wave vectors (by the anisotropy of the crystal) and in a gyrotropic one by the projection of the gyration vector onto the direction of the optical axis.     

Opposite Goos-Hänchen Displacements for TE- and TM-Polarized Beams Transmitting through a Slab of Indefinite Metamaterial

The Goos-Hänchen displacement of a light beam transmitting through an indefinite metamaterial slab is studied. The results indicate that the displacement would be negative or positive for different parameters, and the necessary conditions for negative or positive displacements are summarized. Due to the special anisotropic properties, the directions of displacements for different polarization beams are opposite by proper design. In addition, the simultaneously enhanced positive and negative displacements will appear at different resonant angles under consideration of the active slab. These phenomena could have convenient applications in optical devices.     

Rows of optical vortices from elliptically perturbing a high-order beam

An optical vortex (phase singularity) with a high topological strength resides on the axis of a high-order light beam. The breakup of this vortex under elliptic perturbation into a straight row of unit-strength vortices is described. This behavior is studied in helical Ince-Gauss beams and astigmatic, generalized Hermite-Laguerre-Gauss beams, which are perturbations of Laguerre-Gauss beams. Approximations of these beams are derived for small perturbations, in which a neighborhood of the axis can be approximated by a polynomial in the complex plane: a Chebyshev polynomial for Ince-Gauss beams, and a Hermite polynomial for astigmatic beams.     

Generation of non classical states of light by phase conjugation and parametric conversion

It is shown that oscillators using nearly degenerate parametric conversion or four-wave mixing in the phase conjugation geometry generate pairs of highly correlated photons. The intensity difference of the two corresponding light beams is then expected to be below the shot noise limit. This property can be used to produce intensity stabilized light beams below the quantum limit. The phases of the twin beams also exhibit interesting correlation properties which will be discussed. Moreover, the combination of the twin beams gives a squeezed state, which has been observed by other authors when the device is below the oscillation threshold. We will describe preliminary results of experiments performedabove oscillation threshold.