General considerations in unbalanced fourth-order interference

TL;DR

This paper explores fourth-order interference in unbalanced interferometry setups, revealing conditions where interference persists beyond coherence time limits and extending analysis to pulsed fields, with implications for remote sensing.

Contribution

It provides new insights into unbalanced fourth-order interference effects and extends the analysis to non-stationary pulsed fields, enhancing understanding for sensing applications.

Findings

Interference persists even with large delays exceeding coherence time.

Higher-order interference can be observed in unbalanced paths.

Results are applicable to remote sensing technologies.

Abstract

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