We have defined the degree of coherence 12 (a, ) for two points in the radiation field separated laterally by a distance a and

We have defined the degree of coherence γ₁₂(a, τ) for two points in the radiation field separated laterally by a distance a and longitudinally by a time τ. Under what conditions will this be given by the product of the spatial and temporal degrees of coherence?

Y2(a, T) = y(a)y|| (t). (9.23)