热光的高阶双缝干涉

干涉效应反映了光场的相干性,非相干光源中无序性会破坏干涉.然而对于高阶干涉来说这一看法并不成立.文章作者最近的理论和实验研究表明,横向传播方向无序的热光源可以实现高阶双缝干涉.尽管单个探测器的强度分布是均匀的,处于不同位置的两个探测器的联合强度关联却出现了干涉条纹.当两个探测器同步反向移动时,条纹间距减小为一阶干涉条纹的一半.实验结果同不久前报道的在自发参量下转换过程中产生的纠缠双光子对的双缝实验中所观察到的亚波长干涉效应十分类似.实验结果可以用多模热光场的二阶空间关联性质来解释.热光的高阶双缝干涉是著名的Hanbury-Brown和Twiss实验的空间干涉版本,因此也可称其为Hanbury-Brown和Twiss型双缝干涉。

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.