Spectral Changes of Light and Scattering Phenomena

Alexander Komech

Jia Li, Pinghui Wu, Yali Qin +1 more

Within the validity of the first-order Born approximation, we study the spectrum changes generated by the scattering of light with a tunable spectral degree of coherence (SDOC) from a spatially deterministic medium. Before interacting with the medium, a scalar plane wave is incident upon Young's pinholes, which are employed to produce the incident wave with a tunable SDOC. By assuming that both the scattering potential of the medium and the spectrum of incident plane waves obey Gaussian profiles, the spectrum of the scattered field is derived as a linear combination of Fourier transforms of the scattering potentials. Changes in the spectrum of the scattered field are strongly dependent on the scattering angle, the effective radius of the medium, and Young's pinhole parameter. Moreover, red shifts occurring in the scattered field can be enhanced by either reducing the scattering angle or increasing the effective radius. The results presented here generalize the previous reports, where the light with prescribed functions of the SDOC scattered from a deterministic medium was considered.

E. Wolf, Daniel F. V. James

This paper presents a review of research, both theoretical and experimental, concerning the influence of coherence properties of fluctuating light sources and of correlation properties of scattering media on the spectra of radiated and scattered fields. Much of this research followed a discovery made in 1986, that the spectrum of light may change on propagation, even in free space. More than 100 papers on this topic have been published to date and many of them are reviewed, or at least mentioned, in this article. After an introduction and a summary of some of the main mathematical results relating to second-order coherence theory of statistically stationary optical fields, spectral changes that may take place on superposing fields produced by two partially correlated sources are discussed. Spectral effects in fields produced by two-dimensional secondary sources and by three-dimensional primary sources are then considered. The section which follows describes spectral changes that may arise when polychromatic light is scattered on media whose physical properties vary randomly either in space and/or in time. A review is also presented of recent research, which has revealed that under certain circumstances the changes in the spectrum of light scattered on random media may imitate the Doppler effect, even though the source, the medium and the observer are all at rest with respect to one another. In the final section a brief review is given of a new emerging technique sometimes called spatial-coherence spectroscopy. It is based on the discovery that it is possible, under certain circumstances, to determine field correlations from spectral measurements.

I. S. Burkhanov, Leonid L. Chaikov

The effect of the form change of the intensity correlation function of light scattered back by emulsion or suspension of the particles in liquids is obtained experimentally, when the exciting light intensity increase. The change consists in the appearing in the correlation function of the cosine component with frequency equal to inverse relaxation time of particles concentration fluctuations. The appearance of such cosine component tells about the appearance of the additional spectral line, shifted with respect to exciting light by the half-width of the spectral line of spontaneous polarized Rayleigh scattering by particles. The cosine is caused by beating between exciting radiation and this spectral line. This frequency shift is of about 25-250 Hz depending on particles sizes and characteristic of liquid, in which they are weighted. Together with the scattering relative intensity increase the cosine appearance confirms the obtaining of the stimulated light scattering at variations of the particles concentrations.

Mayukh Lahiri, E. Wolf