Can Two Laser Beams Interfere with Each Other?

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SUMMARY

The discussion centers on the interference of two laser beams and the conditions necessary for their coherent interaction. It emphasizes that for two separate low-intensity lasers to produce an interference pattern, they must be synchronized or "locked" to ensure that no information about the source of individual photons is available. This is crucial for achieving a coherent state similar to that of a single laser in a double-slit experiment. The participants explore the feasibility of having both lasers emit photons simultaneously while maintaining coherence.

PREREQUISITES
  • Understanding of laser physics and coherence
  • Knowledge of the double-slit experiment and its implications
  • Familiarity with photon behavior and wave-particle duality
  • Basic principles of laser synchronization techniques
NEXT STEPS
  • Research laser synchronization techniques, such as phase locking
  • Explore the principles of quantum interference in photon behavior
  • Study the double-slit experiment in detail, focusing on coherence
  • Investigate the effects of low-intensity laser beams on interference patterns
USEFUL FOR

Physicists, optical engineers, and students studying quantum mechanics or laser technology will benefit from this discussion, particularly those interested in the principles of laser interference and coherence.

DParlevliet
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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?
 
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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.
 
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?
 

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