Incoherent Interference

The interference phenomenon of light is a common but most important effect in physics. In this article, we compare and analyse the interference effects of both coherent and incoherent light; in particular, the interference of spatially incoherent light sources is described. Thermal light and a two-photon entangled source may both be regarded as incoherent sources which can generate similar second-order interference effects, but their underlying physics is quite different. First-order interference can be realized with both spatially coherent and incoherent sources in the same well-designed experimental setup, but exhibit different interference patterns; their different interference mechanisms will also be clarified.