Non-classical effects in the statistical properties of light

Measurements on non-classical effects fall into two categories depending on whether the two intensities or photon counts to be correlated refer to a single light beam or to two different beams. The main experimental work in the single-beam case is on resonance fluorescence; the relevant theory is reviewed in some detail, with particular emphasis on the simpler aspects of the calculations. Alternative proposals for generating non-classical single beams by non-linear optical experiments are reviewed more briefly. A similar coverage of double-beam experiments is given, with a detailed account of the theory of non-classical correlations between the light beams generated in two-photon cascade emission, and a briefer survey of corresponding non-linear optical experiments.