Interferometric autocorrelation ($C_{\mathrm{IAC}}(\tau )\propto \int |E(t)+E(t-\tau ){|}^{4}dt$)

A two-replica second-harmonic measurement retaining carrier interference fringes. The formula assumes an instantaneous broad-band second-harmonic response and includes the carrier in $E$. The extra interference information does not in general determine an arbitrary complex pulse uniquely.