Representation of density operators for optical fields having Gaussian quasiprobability functions

For radiation having Gaussian quasiprobability functions, a general method of representation of density operators in terms of outer products of coherent states with nonsingular weight function and only two real variables of integration for every mode is given. It is shown that the representation simplifies, if minimum uncertainty states are used.     

Representation of the photon pathlength distribution in a cloudy atmosphere using finite elements

A new method to derive the photon pathlength probability density function with respect to the photon geometrical path (PDF-GP) is proposed in this paper. This method is based on a finite elements fit of the true PDF-GP using a step function with equidistant intervals. The new method is evaluated based on reference PDF-GPs derived via Monte-Carlo radiative transfer simulations for different single and multilayer clouds with and without surface albedo. The finite elements method was found to perform better than classical Laplace inversion techniques. For the case of two-layer clouds with a thin cirrus cloud (optical thickness 0.5) above a low-level cloud, it is shown that the finite elements method is able to separate the contribution of both cloud layers to the total radiance and, in principle, allows to simultaneously infer cloud top heights of both cloud layers given that enough independent radiance observations at different gas absorption optical depths are taken.     

Design and analysis of coplanar waveguide optical modulator using finite element method

An analysis is given on the finite element method (FEM) for calculating the various parameters of optical modulators and a computer program is written to solve the finite element equation. Based on this method, a Mach-Zehnder type electro-optic modulator with coplanar waveguide (CPW) electrode is designed and fabricated. When compared with the Fourier series method, small differences on the 3-dB bandwidth, characteristic impedance and half-wave voltage, etc. are obtained.     

Multipole pair fields at finite temperature

Finite temperature HFB calculations have been performed in a model using the Surface Delta Interaction as the generating two body force. TheT=0 as well as theT=1 multipole pair fields are studied at various temperatures and different angular momenta. Higher multipole modes appear not only to be more resistant against increasing angular frequency but also against increasing temperature in comparison with the standard monopole pairing mode.     

Characteristic numbers of U1-valued lattice gauge fields

If a U₁-valued latice gauge field u defined on a periodic, 2-dimensional lattice satisfies the generic continuity condition uuuu ≠ − 1, it can be used to construct a principal U₁-bundle over the torus and in that bundle a connection such that parallel transport along bonds is given by u. In higher dimensions this construction can only be carried out if u is monopole-free (otherwise no such bundle can exist). The characteristic classes and numbers of this bundle can then be calculated from u in a straightforward way. Examples are given of u's with maximum possible characteristic numbers, along with a discussion of the behavior of u and of its topology under an action-decreasing deformation.     

Parabolic nondiffracting optical wave fields

We demonstrate the existence of parabolic beams that constitute the last member of the family of fundamental nondiffracting wave fields and determine their associated angular spectrum. Their transverse structure is described by parabolic cylinder functions, and contrary to Bessel or Mathieu beams their eigenvalue spectrum is continuous. Any nondiffracting beam can be constructed as a superposition of parabolic beams, since they form a complete orthogonal set of solutions of the Helmholtz equation. A novel class of traveling parabolic waves is also introduced for the first time.     

Enhanced backscattering of optical vortex fields

The effect of an incident field with a phase screw dislocation (a so-called optical vortex) on the shape of the enhanced backscattering cone was studied theoretically and demonstrated experimentally. We show that the correlation function of the incident field acts as a filter that modifies the shape of the enhanced backscattering cone. The peak value is reduced, and its width is increased as the topological charge of the phase dislocation increases.     

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)].     

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.     

Geophysical gas monitoring using optical techniques: volcanoes, geothermal fields and mines

Optical spectroscopy provides powerful means for studying geophysical gas emissions. An extensive research program in this field has been performed by Swedish researchers in collaboration with European partners during the last 10 years, and a review of the activities and results is given. The techniques suitable for geophysical gas monitoring include the differential absorption lidar (DIAL), differential optical absorption spectroscopy (DOAS), diode laser spectroscopy and gas correlation imaging. Field experiments regarding atomic mercury emissions from geothermal fields were performed with a mobile lidar laboratory in Iceland and in Italy. The atomic mercury concentrations and fluxes from mercury mines were also determined at Abbadia S. Salvatore (Italy) and Almadén (Spain). The volcanic emissions of sulfur dioxide were studied in four ship-borne campaigns concerning the three Italian volcanoes Mt. Etna, Stromboli and Vulcano. Comparisons between the results from the DIAL and passive techniques (DOAS and correlation spectroscopy) were performed. Infrared spectroscopy for geophysical applications is now being developed and will also be discussed.     

Detection of non-paraxial optical fields by optical fiber tip probes

The optical response of a single-mode uncoated fiber tip to a 3D polarized field, including longitudinal components, is investigated. The 3D field is produced by an opportune superposition of TE and TM plane waves. The contribution of the different field components to the detected signals was discriminated by integrating the scanning probe microscope with a multi-heterodyne detection technique. A simple coupling model for the tip is introduced. The longitudinal field component was assumed to couple to the transverse fiber modes through complex coupling coefficients. Coupling coefficients were obtained by fitting the parameters of the model to the experimental data. These results demonstrate that the longitudinal components of the field are coupled by this probe with an efficiency approximately equal to that of the transverse polarization components.     

Dispersion characteristics of complex refractive-index planar slab optical waveguide by using finite element method

In this paper, finite element method (FEM) mode analyses of planar slab optical waveguide having complicated refractive index profile are presented. We try to estimate the dispersion graph, mode cut-off condition, group delay and waveguide dispersion for the case of α-power and chirped-type refractive index profile. In order to obtain the more accurate result, we have derived the higher-order polynomial, which establishes the suitable relationship between b and V for different profile of optical waveguide. On the basis of the derived polynomials, the waveguide dispersion is analyzed for different type of refractive index profile waveguide. Our study shows that the waveguide dispersion can be substantially reduced when we deployed the optical waveguide having linearly chirped-type refractive index profile. Earlier too, the arbitrary refractive index profile has been analyzed but to the best of our knowledge chirped-type refractive index profile has not been analyzed till date for the case of planar slab optical waveguide.     

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.     

有限空间中经典场的正则量子化

从离散的角度研究带边界的1+1维经典标量场和Dirac场的正则量子化问题. 与以往不同的是, 这里将时间和空间两个变量同时进行变步长的离散, 应用变步长离散的变分原理, 得到离散形式的运动方程、边界条件和能量守恒的表达式. 然后, 根据Dirac理论, 将边界条件当作初级约束, 将边界条件和内在约束统一处理. 研究表明, 采用此方法, 不仅在每个离散的时空格点上能够建立起Dirac括号, 从而可以完成该模型的正则量子化;而且, 该方法还保持了离散情况下的能量守恒.     

On the temperature of nonequilibrium optical fields

The dependence of the temperature of single-mode optical radiation on the relative dispersion of the number of photons is investigated. It is shown that the amplitude-stabilized field oscillator has a temperature twice as high as the oscillator excited by a heat source for the same mean energy. Further increase in the temperature of the stationary radiation field is possible by transition to nonclassical states not described by a positive definite quasi-probability function P().Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 7–13, June, 1972.