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B "Mysterious" beamsplitter cube

  1. Nov 12, 2017 #1
    I'm using a non-polarizing beamsplitter cube in an experiment, but it's behaving in an unexpected way. I expected that, if a laser beam enters the cube from one side, ~50% of the beam passes through the cube in the same direction, while ~50% of the beam is reflected and exits the cube at a 90-degree angle. So, one beam entering the cube and two beams exiting the cube.

    Instead, the beam seems to exit the cube in all 4 directions: passing through, exiting left, exiting right, and even being reflected back to the source. Is this expected behavior? What is causing it?

  2. jcsd
  3. Nov 12, 2017 #2


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    What about the intensities ?
    Last edited: Nov 13, 2017
  4. Nov 12, 2017 #3
    I didn't measure intensities, but, visually, the beams along the two "expected" axes look ~50% stronger.
  5. Nov 12, 2017 #4


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    Internal reflections off of the glass-air boundary will likely reflect part of the beam out of the other two faces, but the intensities should be fairly weak.

    Don't trust your eyes. They aren't very good measuring devices. This is a known problem with the version 1.0's and I'd replace them as soon as the first upgraded models come out. :rolleyes:
  6. Nov 13, 2017 #5

    Andy Resnick

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    I've noticed a similar phenomenon, in my case it seems to be an 'alignment' problem- using a different input face may fix the problem. The manufacturer may place a marking on the cube to help alignment, I'm not entirely sure how these devices work:

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