Unbalanced fourth-order interference beyond coherence time

Interferometry has been used widely in sensing application. However, the technique is limited by finite coherence time of light sources when interference paths are not balanced. Higher-order effects involve intensity correlations between multiple detectors and may have advantage over traditional second-order effect exhibited only one detector. We discuss various scenarios with unbalanced delays different fourth-order coincidence two detectors. find, some cases, persists even much larger than sources. also extend discussion to nonstationary pulsed fields, which need consider pulse shape require a treatment. These results will be useful remote applications.