Interference of nonlinear optical signals generated by multimode lasers: analogy to holography by incoherent light

We examine how two nonlinear optical signals generated by a multimode laser will interfere. This interference is shown to be analogous to linear interference with partially coherent light. Consequently, we demonstrate an interferometric method for determining the temporal and spatial coherence of a laser, which features no moving parts and does not require precise ultrashort mechanical translations.