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If a laser beam is refracted and exits from the other side, and we project another laser beam so that it is reflected in the refraction of the first ray (regardless of the reflected half of the first and the refracted half of the second), will the two combine (make constructive interference) ? Will it still be possible even if we reduce the laser amplitude to very small values? For example ($10^{-6}$) or is it difficult to achieve

FOXDeveloper
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    What, specifically, do you mean by 'combine'? Clearly one can arrange the two beams to be generally collinear (how precise depends on how much work you put into it). Many of us have likely done that to, e.g., have a visible alignment beam along the beam path of an IR laser... – Jon Custer Mar 06 '23 at 21:14
  • I mean Constructive interference , It could happen even theoretically ? – FOXDeveloper Mar 06 '23 at 21:27
  • Really only if both beams are from the same laser, and the total path length is shorter than the coherence length. – Jon Custer Mar 06 '23 at 21:29
  • Could you add your comment about constructive interference to the question (edit it) and perhaps @JonCuster could then write a brief answer explaining why – StephenG - Help Ukraine Mar 06 '23 at 22:42

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Large telescopes do this kind of combining routinely. They combine starlight, not lasers.

A telescope can resolve finer details if it has a larger mirror. It is very hard to make a perfect mirror for visible wavelengths larger that a few meters. It is also very hard to make multiple smaller mirrors and line them up so accurately that the combined light is the same as if it had come from one large mirror. It turns out the second way is easier though. So all modern large telescopes use it. You can see it in the segmented mirror of the James Webb Space Telescope. See https://webb.nasa.gov/content/observatory/ote/mirrors/index.html

Optical telescopes use optical components similar to what you have drawn to combine images.

enter image description here

Radio telescopes work with much longer wavelengths, so it is easier to combine them with the required accuracy. On the other hand, the required diameters are also much larger. enter image description here

It is possible to digitize radio signals and combine them in a computer.

For more, see this page from ESO - Interferometry

mmesser314
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