  A third-order double-slit interference experiment with pseudo-thermal light
source in the high-intensity limit has been performed by actually recording the
intensities in three optical paths. It is shown that not only can the visibil-
ity be dramatically enhanced compared to the second-order case as previously
theoretically predicted and shown experimentally, but also that the higher
visi- bility is a consequence of the contribution of third-order correlation
interaction terms, which is equal to the sum of all contributions from
second-order cor- relation. It is interesting that, when the two reference
detectors are scanned in opposite directions, negative values for the
third-order correlation term of the intensity fluctuations may appear. The
phenomenon can be completely explained by the theory of classical statistical
optics, and is the first concrete demonstration of the influence of the
third-order correlation terms.
