High-order double-slit interference of thermal light

From a common viewpoint, interference is related to the coherence of the optical field, and the disorder of a light source may destroy the interference fringe. But this is not true for high-order interference. Our recent theoretical and experimental studies show that a thermal-like light source that is random in transverse propagating directions can perform high-order double-slit interference. Though the intensity distribution measured by each detector is homogeneous, an interference fringe emerges in the joint-intensity measurement of two detectors placed at different positions. When the two detectors are scanned synchronously in opposite directions, the fringes show a half period for the first-order interference, exhibiting so-called subwavelength interference, similar to the results for entangled photon pairs generated in spontaneous parametric down-conversion. The experimental results can be explained with the second-order spatial correlation of a multimode thermal optical field. The present work can be regarded as a new version of the landmark Hanbury Brown and Twiss (HBT) experiment, and in this sense we may call it an HBT-type double-slit interference.