Partially Coherent Light

Abstract

When discussing the theory of interference and diffraction of waves, one usually assumes that the fields remain perfectly sinusoidal for all values of time. This is obviously an idealized situation and we know that the radiation from an ordinary light source consists of finite* size wave trains, a typical time variation of which is shown in Fig. 5.1. As can be seen from the figure, the electric fields at times t and t + Δt will have a definite phase relationship if Δt ⪡ τ_C and will (almost) never have any phase relationship for Δt ⪢ τ_C, where τ_C represents the average duration of the wave trains (see Fig. 5.1).