Diffraction method for recording optical wave fields

We propose a method for recording an optical wave field that is based on diffraction of the optical wave field by two screens that are complementary to each other. We show that the new method ensures the measurement of the phase of the wave field with a high accuracy and spatial resolution. An optical scheme for implementing the diffraction method and an algorithm for reconstructing the phase of the wave field from the measurement data are developed. We perform a computer simulation of the experiment on recording the optical wave field based on the method proposed.     

Raster method for recording optical wave fields

We propose a new method for recording the wave field. The method is based on that the angular spectrum of the field is modulated using an amplitude mask. It is shown that the new method ensures high spatial and angular resolutions. An optical scheme for implementing the method and an algorithm for reconstructing the wave-field phase from the measurement data are developed. Computer simulation of the experiment for recording the wave field on the basis of the proposed method is performed.     

无衍射特殊光束的产生与三维表征

无衍射光束(如贝塞尔光束、艾里光束)因具有无衍射、自愈合的特性, 在很多领域都有广泛的应用. 本文提出使用纯相位型空间光调制器对光场的复振幅进行调控, 从而可以产生多种复杂模式的无衍射光束, 如强度可独立调控的多个零阶贝塞尔光束, 两个高阶贝塞尔光束干涉生成的花瓣状无衍射光束, 具有多个主瓣的加速光束等特殊的无衍射光束. 通过在待测焦场附近放置一个平面反射镜, 使其沿光轴快速扫描光场, 并由数字相机同步拍摄反射回来的一系列二维光场强度分布信息, 可实现对无衍射光束三维光场强度分布的快速测量和表征. 本实验方法和技术可以快速产生各种复杂的特殊光场并获得其精确的三维可视化重建效果, 在光学显微、光学俘获、光学微加工等领域有潜在的应用价值.     

Holographic generation of a class of nondiffracting fields with optimum efficiency

We discuss the accurate generation of complex optical fields using phase holograms that provide the optimum diffraction efficiency. In each considered case, the phase modulation of the employed hologram is identical to the phase of the desired optical field. We show that periodic and quasiperiodic nondiffracting optical fields, mathematically obtained through the superposition of multiple plane waves, can be generated with high fidelity using this approach.     

A unified optical theorem for scalar and vectorial wave fields

The generalized optical theorem is an integral relation for the angle-dependent scattering amplitude of an inhomogeneous scattering object embedded in a homogeneous background. It has been derived separately for several scalar and vectorial wave phenomena. Here a unified optical theorem is derived that encompasses the separate versions for scalar and vectorial waves. Moreover, this unified theorem also holds for scattering by anisotropic elastic and piezoelectric scatterers as well as bianisotropic (non-reciprocal) EM scatterers.     

Parabolic oxidation of metals in homogeneous electric fields

A previously proposed thin film parabolic growth law (Fromhold, 1963) is extended to include film growth due to any number of diffusing defect species of arbitrary valence, and an analysis is made of the effects of applying external electrostatic potentials during oxidation. The total electrical conductivity and the partial conductivities are markedly position-dependent in the protective film, varying by orders of magnitude from one interface to the other. The built in electrostatic potential across the film is independent of thickness of the film and is a function of the partial conductivities of the diffusing ionic and electronic defect species. Effects of electrical shorting of the oxide film by external circuitry are analyzed. Depending on polarity, a constant applied potential can increase or decrease the rate constant but does not alter the kinetics from the parabolic form, in accordance with published experimental data. The net electrostatic potential required to stop metal oxidation is derived for the model in question. For growth by a single ionic species, the stopping potential is that electrostatic potential which gives an equal electrochemical potential at the metal-oxide and the oxideoxygen interfaces. For growth by multiple ionic species, the stopping potential is a function of the ionic partial conductivities.     

Experimental investigation of local properties and statistics of optical vortices in random wave fields

We present the first direct experimental evidence of the local properties of optical vortices in a random laser speckle field. We have observed the Berry anisotropy ellipse describing the anisotropic squeezing of phase lines close to vortex cores and quantitatively verified the Dennis angular momentum rule for its phase. Some statistics associated with vortices, such as density, anisotropy ellipse eccentricity, and its relation to zero crossings of real and imaginary parts of the random field, are also investigated by experiments.     

Real-time holograms generated by second-harmonic cross correlation of object and reference optical wave fields

Three-dimensional holographic images of extended diffusing objects are simultaneously recorded and reconstructed by optical cross correlation in a second-order nonlinear crystal. An interaction geometry in which the phase-matched object and reference fields propagate slightly noncollinearly is particularly convenient for producing these second-harmonic-generated holograms.     

Friedmann universes containing wave fields

In this paper the Friedmann universes containing(i) a massless real scalar field,(ii) a massive real scalar field,(iii) electromagnetic fields,(iv) the combined massive complex scalar and electromagnetic fields are investigated. In(i) the field has to be either purely spatial or else purely temporal and the latter case is completely solved. Similarly in(ii) the purely time-dependent case has been reduced to a single fourth order ordinary differential equation. In this case graphs of the numerical solutions have been exhibited. In(iii) as expected, no non-trivial solution exists. In(iv) all possible cases are studied. In case the complex wave function is a product of two non-constant functions, i.e. ψ=ξ(r)τ(t), there exists no solution. In the subcase gx(r)=ξ^*(r)=constant, ¦τ(t)¦=constant the problem is completely solved. In the subcase ξ(r)=ξ^*(r)=constant and ¦τ(t)¦ is non-constant, the system of equations boil down to the same fourth order ordinary differential equation as mentioned before. In the last two sub-cases, the time-dependent wave field carries electric charge density which, strangely enough, is decoupled from the electromagnetic fields.     

Interference of traveling nondiffracting beams

We study numerically the interference resulting from the superposition of two Bessel beams propagating in free space. We discuss how to obtain such beams and show the existence of the self-imaging effect during propagation. The evolution of the superimposed Bessel beams is analyzed on the basis of the evolution of the individual beams. Our exact numerical predictions contradict previous approximated analytical treatments, showing that they can lead to quantitatively wrong results and misleading conclusions.     

Conversion of bright nondiffracting beams into dark nondiffracting beams by use of the topological properties of polarized light

We present a method for the generation of an axial phase dislocation on a wave front, which is induced by topological properties of polarized light. This effect is shown to be useful for conversion of bright nondiffracting beams into dark nondiffracting beams. Experiments showing the generation of dark nondiffracting beams have been performed.     

Stochastic transport in random wave fields

An analysis is made of particle diffusion and the field of a passive impurity in random wave fields. A characteristic of this problem is that the statistical transport coefficients (diffusion coefficients) vanish in the approximations normally used (delta-correlated random field or diffusion) giving the Fokker-Planck equation. In this study perturbation theory is used in the first nonvanishing order of smallness which allows these transport coefficients to be calculated for waves of various types.     

Elliptic vortices of electromagnetic wave fields

We demonstrate the existence of elliptic vortices of electromagnetic scalar wave fields. The corresponding intensity profiles are formed by propagation-invariant confocal elliptic rings. We have found that copropagation of this kind of vortex occurs without interaction. The results presented here also apply for physical systems described by the (2+1) -dimensional Schr?dinger equation.     

Nonlinear optical terahertz wave sources

We developed a Cherenkov phase-matching method for monochromatic THz-wave generation using the DFG, process with a lithium niobate crystal, which resulted in both high conversion efficiency and wide tunability. Although THz-wave generation by Cherenkov phase matching has been demonstrated using femtosecond pumping pulses, producing very high peak power, these THz-wave sources are not monochromatic. Our method generates monochromatic and tunable THz, waves using a nanosecond pulsed laser source. We also show that Cherenkov radiation with waveguide structure is an effective strategy for achieving extremely wide tunable THz-wave source. We fabricated MgO-doped lithium niobate slab waveguide and demonstrated difference frequency generation of THz-wave generation with Cherenkov phase matching. Extremely frequency-widened THz-wave generation, from 0.1 to 7 THz was observed.     

A new type of optical fields

New fields possessing the peculiar property of propagating in the form of thin blades of light are introduced. They are shown to be generated by suitable anisotropic gaussian Schell-model sources. A simple explanation of the behavior of these fields is given by representing them as a superposition of mutually uncorrelated, spatially displayed coherent fields.     

Entropy of generalized Gaussian optical fields

We consider two definitions of entropy: thermodynamic entropy and signal entropy. We compare their value for the class of generalized Gaussian fields. The first definition is well adapted to monomode stationary fields, while the second one is bounded only for multimode fields. We prove that these two notions are definitely different, for example, the real Gaussian field has a maximum signal entropy and a minimum thermodynamic entropy (among the Gaussian fields).     

Information content of optical vortex fields

We study, experimentally as well as theoretically, the spatial coherence function and the Wigner distribution function for one-dimensional projections of optical vortices of different orders. The information entropy derived from the spatial coherence functions has been used to quantify the information content of the vortices and compared with those obtained for the Gaussian beam. The experimental results verify the theoretical findings of Agarwal and Banerji [Opt. Lett. 27, 800 (2002)].     

Generalized expression for optical source fields

A generalized optical beam expression is developed that presents the majority of the existing optical source fields such as Bessel, Laguerre–Gaussian, dark hollow, bottle, super Gaussian, Lorentz, super-Lorentz, flat-topped, Hermite–sinusoidal-Gaussian, sinusoidal-Gaussian, annular, Gauss–Legendre, vortex, also their higher order modes with their truncated, elegant and elliptical versions. Source intensity profiles derived from the generalized optical source beam fields are checked to match the intensity profiles of many individual known beam types. Source intensities for several interesting beam combinations are presented. Our generalized optical source beam field expression can be used to examine both the source characteristics and the propagation properties of many different optical beams in a single formulation.