Interference of fields emitted spontaneously at different times

We report the first observation of interference in the spontaneous parametric down conversion (SPDC) radiation emitted at different time moments. SPDC is a nonlinear optical process in which a higher energy UV pump photon splits into two daughter photons (usually called signal and idler) inside a noncentrosymmetric crystal when the phase matching condition is satisfied. For the experimental setup, we used two temporally separated pump pulses generating SPDC in a type II BBO crystal.