Emil Wolf

Frequency shifts of spectral lines produced by scattering from spatially random media

Scattering of polychromatic light by a medium whose dielectric susceptibility is a random function of position is considered within the accuracy of the first Born approximation. It is shown, in particular, that if the two-point spatial correlation function of the dielectric susceptibility has Gaussian form and the spectrum of the incident light has a Gaussian profile, the spectrum of the scattered light may be shifted toward the shorter or the longer wavelengths, depending on the angle of scattering. The results are analogous to those derived recently in connection with radiation from partially coherent sources [ Nature (London)326, 363 ( 1987)].

Field correlations within a completely incoherent primary spherical source

Spectral correlation properties of the field within a primary delta-correlated, scalar, spherical source are investigated. It is found that the field at any two source points is correlated over distances of the order of a wavelength, at least in the case when one of the points coincides with the center of the source. In the asymptotic limit when the radius of the source is large compared with the wavelength, the field distribution becomes statistically homogeneous and the degree of spectral coherence at any two source points is given by (sin kr)/kr, where r is the distance between the two points and k is the wave number.

Partially coherent sources that generate the same far-field spectra as completely incoherent sources

It is shown that one can specify a broad class of three-dimensional, primary, quasi-homogeneous sources, each of which will generate a field whose spectrum throughout the far zone is identical with that produced by a spatially completely incoherent source. Neither the incoherent source nor such an “equivalent” source need be isotropic, and the spectral correlation length of the quasi-homogeneous source can be arbitrarily large, provided that it is much smaller than the linear dimensions of the source.

Scattering of Electromagnetic Fields of Any State Of Coherence from Fluctuating Media

Much of the existing literature on the theory of light scattering from fluctuating media is restricted to either monochromatic incident fields,1 or to quasimonochromatic incident fields which are spatially coherent over the entire scattering volume.2,3

Field Correlations And Spectra Produced By Locally Incoherent Primary Sources

In this paper the correlation properties (in the space-frequency domain) and spectra of wavefields produced by a class of sources which occupy a finite domain and are locally incoherent, i.e., by finite sources which are correlated only over distances which are small compared to the wavelengths of interest, are investigated. For points inside the source the complex degree of spectral coherence and the spectrum of the field are investigated. For points in the far zone of the source the spectrum of the field is studied.