 Two-line coherence beating

Two equally intense monochromatic spectral components have normalized first-order optical coherenceThe visibility zeros occur at $\tau =(2j+1)\pi /|\Delta \omega |$, while its revivals repeat every $2\pi /|\Delta \omega |=1/|\Delta \nu |$. This envelope describes self-interference of each spectral component after a delay, not a time-resolved measurement of inter-frequency beating at one fixed point. Unequal line intensities prevent complete cancellation at the minima.