Can Two Laser Beams Interfere with Each Other?

[DParlevliet]

I have a question about this old (closed) Thead about the quote:

"...but also two separate very low intensity laser beams have been sent through single slits to a common detector and a diffraction pattern resulted. The intensity was so low that the probability of a (semi-classical) photon being between the slits and the screen was close to zero." (from Oz)

I suppose two lasers don't each emit a photon at the same time. So if one photon is emitted by one laser (and not by the other laser) with which wave does the photon interfere?

 

[jtbell]

My understanding is that in such an experiment, the two lasers have to be coupled or "locked" to each other in such a way that there is no information about which laser any individual photon comes from. This makes it analgous to a double-slit experiment with a single laser as a source, in which there is no information about which slit any individual photon passes through.

 

[DParlevliet]

Two lasers must be synchronizes to be sure that the photons has the same phase. But can lasers be locked that both also emit a photon at the same time?