Abstracts Category : Other

On spectroscopy of partially coherent light

by Daniel Francis James

In the past few years there has been a good deal ofresearch into a novel mechanism which gives rise to a change in thespectrum of a wave field with respect to the spectrum of thesource, even though the field may be propagating in free space, andthe source and observer are not in motion with respect to eachother. This new effect is collective in nature: on a microscopiclevel, individual photons do not change energy. The spectralmodulations are a result of the statistical nature of thefluctuations of the source. This thesis presents an investigationof certain aspects of this phenomenon. </br>Afterbriefly reviewing some of the basic concepts in the theory ofpartially coherent light, a theoretical analysis of radiation frommodel partially coherent sources is presented. Two importantclasses of sources are considered: primary sources (e.g.charge-current distributions) and secondary sources (e.g.illuminated apertures). </br>The effect of thespatial coherence properties on the spectra of fields is discussedin some detail in connection with Young's interference experiment.A possible application of such spectral effects is also discussed.It is shown that spectral analysis, rather than fringe visibilitymeasurements can be used to determine correlation properties of thefield. A principle is also formulated, according to which, in manyinterferometric measurements a trade-off can be made between thelength of the base line and the frequency at which measurements aremade. This principle, when applied to the proposed method ofdetermining correlation properties of the field might form thebasis of a novel method of aperture synthesis imaging. </br>Finally we discuss how spatial coherence canarise in atomic systems. A model radiating system consisting of twointeracting atoms is analyzed. Explicit expressions for the degreeof coherence, the source spectrum and the spectrum of the radiationfield are derived. The results show that, for atomic systems, thespectra modification due to source coherence can be considered interms of a multiple-atom analogue of the effects of radiationreaction on a single atom, i.e. the spontaneous decay and the Lambshift.