Two-photon interference with non-identical photons

• Two-photon interference with non-identical photons is studied based on the superposition principle in Feynman's path integral theory.
• The second-order temporal beating between laser and pseudothermal light beams is reported.
• The method to observe two-photon interference with photons of different colors is suggested.

Two-photon interference with non-identical photons is studied based on the superposition principle in Feynman's path integral theory. The second-order temporal interference pattern is observed by superposing laser and pseudothermal light beams with different spectra. The reason why there is two-photon interference for photons of different spectra is that non-identical photons can be indistinguishable for the detection system when Heisenberg's uncertainty principle is taken into account. These studies are helpful to understand the second-order interference of light in the language of photons.