摘要:

For a point source of light within the near field of circular, elliptical or tilted circular discs, diffraction into the geometrical shadow region is studied theoretically. For observation in the near field on the shadow side of the disc, the geometry of the caustic formed is shown to be closely approximated by the evolute of the diffracting edge, a result which holds strictly for plane wave incidence. For observation in the far field, the quite different patterns observed by Coulson and Becknell are explained using two approaches. First, a suitable approximation to the phase term in the Kirchhoff integral leads to a largely analytical treatment of the circular disc, and for the field on the axis of the elliptical disc. Second, the field away from the axis for the elliptical disc is explained by applying stationary phase methods to the Rubinowitz edge integral, in a modified form which is uniformly valid across the shadow boundary. Finally, the behaviour of wavefront dislocations formed in the diffracted field is studied.

ISSN:0030-3909    

DOI:10.1080/713821175

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The dark-field, empty-field and instrument accommodations were measured for a number of emmetropic and ametropic subjects to investigate (1) the natural individual variation in these accommodation levels, (2) correlations and regressions between some of the variables, (3) the effect of refractive error on the anomalous accommodation levels and (4) response times to dark- and empty-field conditions. The results show that (a) some subjects have highly stable dark and empty-field accommodation levels, but others exhibit significant fluctuations, (b) dark- and empty-field accommodation levels have a high correlation and regression, but dark-field and instrument accommodations correlate less well, and (c) some subjects respond quickly to the dark- and empty-field conditions, whereas others have response times of several minutes.

ISSN:0030-3909    

DOI:10.1080/713821177

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Using 1-D and 2-D (circular) prolate spheroidal wave functions ϕn(c,x) and ϕN,n(c,r) exp (iNϕ), the paper discusses the imaging by an optical system of a partially coherent light field produced by an extended incoherent quasi-monochromatic source. The process mechanism of the degrees of freedom transmission through 1-D and 2-D optical systems are explained in terms of two integral equations with respect to the illuminating system and imaging system and an expression for the degrees of freedom is developed.

ISSN:0030-3909    

DOI:10.1080/713821190

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

In this paper we study the statistical properties of the reconstructed object wavefunction of a weak phase-amplitude object from two low-dose image intensity distributions. The images are obtained by successively illuminating the object coherently by plane quasi-monochromatic waves which make different angles with the optical axis. The case is discussed for isoplanatic conditions and one lateral dimension. Explicit expressions of the mean and variance of the reconstructed wavefunction are presented in terms of the illumination dose. The low spatial frequencies which were hardly retrievable in the method based on two defocused images obtained under axial illumination are accessible in this approach.

ISSN:0030-3909    

DOI:10.1080/713821184

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A general method is described for optimizing the groove profiles of perfectly conducting gratings. The functional derivatives of the coefficients of the diffracted far field are first introduced, and it is shown that these derivatives provide all the necessary information on the ‘local’ relationship between the far field and the groove profile. The principle of several well-known minimization algorithms is recalled, and numerical examples are given which show the versatility and the efficiency of the method. Numerous extensions of the method seem to be straightforward, especially for gratings of finite conductivity.

ISSN:0030-3909    

DOI:10.1080/713821181

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor