One- and two-photon interference from two temporally separated laser pulses

Summary form only given. According to Feynman, quantum mechanics teaches us that interference occurs when the relevant amplitudes become indistinguishable. In the case of first-order and second-order interference (order by "intensity"), the relevant amplitudes are one-photon and two-photon amplitudes, respectively. We report a quantum interference experiment in which the relevant amplitudes are associated with temporally well separated laser pulses. Both first- and second-order interference are observed under certain different conditions. The experimental setup is shown where a BBO crystal is pumped by two short UV laser pulses.