It seems that if the coherence length of a laser is big enough, it is possible to observe a (moving) interference picture by combining them. Is it true? How fast should photo-detectors be for observing of the interference of beams from two of the "best available" lasers? What is the coherence length of the best-available laser? More specifically, does there exist any (optical single-wavelength) laser with coherence length exceeding 500 meters?
Optics – Is it Possible to Observe Interference from 2 Independent Optical Lasers?
laseroptics
Best Answer
This paper seems relevant to your question. If I'm reading the abstract correctly, the answers to your questions are:
A: Yes
A: 1 millisecond or faster
A: More than 300 km
A: Yes
The abstract in the paper:
An interesting 1986 review of interference from independent sources:
"Interference between independent photons", Rev. Mod. Phys. 58, 209–231 (1986)