Measurement of the two-photon time distribution in a mixture of light from a He-Ne laser and a Gaussian source of the same central frequency agrees well with the prediction of coherence theory when the laser is represented by a single coherent state. The peak in the distribution near zero time difference is made up of contributions due to the second-order interference between pairs of Gaussian photons and between laser and Gaussian photons.
G. Present and D. B. Scarl, "Two-Photon Correlations in a Mixture of Gaussian and Laser Light," Appl. Opt. 11, 120-124 (1972)