I'm passing a 1392nm laser through a beamsplitter, through an aresol medium hitting a retroreflector, passing back through an aresol medium, and passing it through the same beamsplitter. The two beams split toward two respective photodiodes, and the final transmitted beam is irrelevant; the laser has an isolater, so it won't be damaged. The purpose is to measure light extinction in the aresol medium. If the two beams are reflected directly back at each other, will there be any interference between the two beams and possibly lost data? Personally, I don't think so, but others I work with have this concern, and it will take a lot more time and tedium to align the laser if I don't pass the beam back through itself.
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$\begingroup$ The concept I was concerned about is coherence. If the beams are spatially or temporally coherent, interference can occur. However, on the scale of the experiment I'm running, coherence isn't a concern. $\endgroup$– ReedCommented Aug 6, 2020 at 22:54
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There should not be any lost data due to the two beams counterpropagating on the same path. The most likely problems will be due to imperfect isolation, depolarization in the aerosol, and imperfect characteristics of the retroreflector.
The retroreflector in particular is likely to produce return rays that are offset from incident rays by a distance greater than the average size or separation of the aerosol droplets.
