Two-photon interference with two independent and tunable single-mode continuous-wave lasers

The second-order temporal interference between two independent single-mode continuous-wave lasers is discussed by employing two-photon interference in Feynman's path integral theory. It is concluded that whether the second-order temporal interference pattern can be retrieved via two-photon coincidence counting measurement is dependent on the relationship between the resolution time of the detection system and the frequency difference between these two lasers. Two identical and tunable single-mode diode lasers are employed to verify the predictions experimentally. The experimental results are consistent with the theoretical predictions. These studies are helpful to understand the physics of two-photon interference with photons of different spectrums and application of two-photon interference in quantum information processing.