It is shown that the visibility of multi-photon interference for classical sources grows rapidly with the order of interference. For three-photon and four-photon interference of two coherent sources, the visibility can be as high as 81.9% and 94.4%, respectively, - much higher than the 'classical limit' of two-photon interference (50%). High-visibility three-photon and four-photon interference has been observed in experiment, for both coherent and pseudo-thermal light.
@article{arxiv.0705.0854,
title = {High-Visibility Multi-Photon Interference of Classical Light},
author = {I. N. Agafonov and M. V. Chekhova and T. Sh. Iskhakov and A. N. Penin},
journal= {arXiv preprint arXiv:0705.0854},
year = {2007}
}