ISSN:0030-3909    

DOI:10.1080/713821142

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

It is shown that under certain conditions the speckle due to transillumination of a diffuser under partially space coherent light recorded in two neighbouring planes remains correlated.

ISSN:0030-3909    

DOI:10.1080/713821141

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

ISSN:0030-3909    

DOI:10.1080/713821143

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Cross-beam laser velocimetry using Bragg shift and photon correlation has been utilized to measure a weak secondary flow component in the presence of strong primary flow at right angles to it. To obtain this velocity component with adequate accuracy, the apparent Doppler frequency was determined by Fourier transformation of the correlogram followed by two steps of interpolating correction. The remaining frequency error may be as little as 10-2jfwhere integral multiples of jfare the abscissa values for which the discrete Fourier transform is given. Finally a method is described which allows precise orientation of the cross-beam fringes at right angles to the secondary flow component; it makes use of symmetry properties of the flow in question.

ISSN:0030-3909    

DOI:10.1080/713821144

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Estimator variances of photon correlation and structure functions can be calculated exactly for gaussian-lorentzian light if the total experimental duration is large compared with the coherence time. For low photon count rates, the correlation function consistently shows the better noise performance. At high mean count rates, the structure function gives the faster estimate, particularly for the high-frequency part of the signal. This suggests the usefulness of photon structure functions for diffusion measurements on highly polydisperse systems.

ISSN:0030-3909    

DOI:10.1080/713821145

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

By comparing the zero-order diffraction intensity of a polarized light beam after it has passed through a magnetic thin film in the (i) normal and (ii) saturated states, we have been able to measure the degree of coherence of the light beam. The results from these magneto-optic measurements have been compared to those obtained from the classical two-slit diffraction pattern; very good agreement is obtained.

ISSN:0030-3909    

DOI:10.1080/713821149

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Image processing systems that contain feedback loops sometimes become unstable: they oscillate in space and time, which is fascinating but undesirable. These oscillations can be avoided if the system satisfies certain stability conditions. For purely time-dependent (one-dimensional) linear systems some stability tests are known, for example, from electronics. In this paper we consider multidimensional (space/time) systems. The resulting stability theorems are applied to some examples, such as iterative image processing, analog computing, etc. Finally, some considerations for the treatment of nonlinear systems are given.

ISSN:0030-3909    

DOI:10.1080/713821139

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A new type of filter called the optimum circular symmetrical filter (OCF), described in a previous paper, is used for digital and optical pattern recognition. This rotation-invariant matched filter optimizes the signal-to-noise ratio. Optical experiments with letters of the alphabet gave results that agreed with the digital simulation.

ISSN:0030-3909    

DOI:10.1080/713821147

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Some features of contrast improvement by low-frequency attenuation are described on the basis of a one-dimensional model. The properties deduced are verified experimentally in a coherent image-enhancement system. A rigid mixture of fluorescein in orthoboric acid is used as a spatial filter. Its photo-induced change permits variable optical density of the filter as well as variable filter dimensions in the spatial frequency plane.

ISSN:0030-3909    

DOI:10.1080/713821150

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

An efficient method for computing diffraction integrals is presented. It is based on an idea put forward by Hopkins [1]. The integration domain is divided into subdomains, in each of which the phase and amplitude are approximated by simple functions which make it possible to evaluate the resulting integral in terms of known functions. While Hopkins employed a linear approximation to the phase and a constant approximation to the amplitude, we here approximate both the phase and the amplitude by parabolas. A comparison of the results of our method with those of Hopkins's method shows that our method requires fewer subdomains and less computation time to yield a desired accuracy. Another advantage of our method is that it can be applied to apertures of a general shape without significant loss of accuracy.

ISSN:0030-3909    

DOI:10.1080/713821140

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor