摘要:

A general modal theory of scalar wave scattering by periodic surfaces is developed in which the field within the grooves is expanded in modes and the diffracted field in a Rayleigh expansion. The scattering-matrix is shown to be explicitly unitary and to satisfy the reciprocity condition, and the behaviour of the order- and mode-amplitudes at the lowest threshold is deduced. An abstract operator formulation of the theory clarifies its basic structure.

ISSN:0030-3909    

DOI:10.1080/713820236

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

We propose a new formulation of Miller's regularization theory, which is particularly suitable for object restoration problems. By means of simple geometrical arguments, we obtain upper and lower bounds for the errors on regularized solutions. This leads to distinguish between ‘Hölder continuity’ which is quite good for practical computations and ‘logarithmic continuity’ which is very poor. However, in the latter case, one can reconstruct local weighted averages of the solution. This procedure allows for precise valuations of the resolution attainable in a given problem. Numerical computations, made for object restoration beyond the diffraction limit in Fourier optics, show that, when logarithmic continuity holds, the resolution is practically independent of the data noise level.

ISSN:0030-3909    

DOI:10.1080/713820228

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

In this, the first of two papers on the subject, we present an analysis of a non-linear optical system with a mode coupled to its second harmonic, exhibiting a rich variety of non-equilibrium steady-state transitions. Here we use a semiclassical analysis to examine the steady states and their stability, and thus predict the existence of various instabilities. We find that this system exhibits both first- and second-order phase transition-like behaviour, as well as having a hard mode transition. The application of this system as a switching device is also considered.

ISSN:0030-3909    

DOI:10.1080/713820226

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The problem of simultaneously computing aberration and diffraction effects in optical systems is treated by using Green functions of the scalar wave equation. The multidimensional integral which describes image quality is evaluated by the method of stationary phase and is seen to give an explicit set of recursion relations for the propagation of different wave components. The zeroth order approximation of the integral gives ray tracing results and a gaussian approximation includes diffraction effects.

ISSN:0030-3909    

DOI:10.1080/713820235

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0030-3909    

DOI:10.1080/713820232

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Images of high quality can be obtained with a narrow annular aperture by image processing. A reformulation of a correction process currently in use with a radio astronomy imaging ring shows that any desired point spread response or beamshape may be obtained by a process involving Chebychev polynomial expansions.

ISSN:0030-3909    

DOI:10.1080/713820231

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The statistical characterization of the inhomogeneity of a medium which may exhibit both local and overall anisotropy is investigated. Such a medium may be completely described statistically by the mean and autocovariance of the magnitude which describes the inhomogeneity, as long as its values are normally distributed. Assuming the inhomogeneity to be described by the permittivity, expressions for the mean and autocovariance are derived. For an anisotropic medium these parameters are second rank tensors, and it is found that they may be represented as diagonal matrices in a coordinate system based on the symmetry axes of the material. Finally, an expression for the autocovariance function of the orientation is derived from the general autocovariance function of the permittivity.

ISSN:0030-3909    

DOI:10.1080/716099506

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The scattering of an electromagnetic wave by an inhomogeneous medium is considered as arising solely due to spatial variation of the electric permittivity. The wave equation in the medium is solved for the Fraunhofer region using the first Born approximation. The assumption is made that the medium possesses macroscopic isotropy but allows local anisotropy (on a molecular level). In the light scattering experiment, the relationships between the autocovariance tensor for the medium and the scattered intensity observed is studied.

ISSN:0030-3909    

DOI:10.1080/716099506a

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

This paper presents a study of the nonlinear propagation of a mixture of two degenerate modes (TEM00and TEM10) of a high power laser beam in a collisional plasma. The non-linear dependence of the dielectric constant inside the collisional plasma is due to non-uniform redistribution of carriers on account of their inhomogeneous heating. The focusing effects have been studied for different power ratios of the two modes and the absorption effects have also been considered. In certain power regions considered the beam either converges or defocuses in both the directions, while in some other defined regions of the power spectrum one dimension of the beam focuses and the other defocuses.

ISSN:0030-3909    

DOI:10.1080/713820244

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The excitation of the system ofNtwo-level atoms is considered with the pulse of the resonance quantum field in the state with the definite number of photonsnbn> (n≫1). It is shown that the atomic system may be excited into the superradiant correlated (radiation proportional toN2) but noncoherent (macroscopic polarization is zero) state.

ISSN:0030-3909    

DOI:10.1080/713820225

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor