I'm working with a Sagnac interferometer. To split a laser beam (He-Ne), we are using a cubical, non-polarizing beam splitter from Thor Labs (BS031).

The beam splitter is fastened to a stand that is set to the height of the incoming laser beam using a simple clamp. I think I fastened the clamp too hard because there is clearly a small shattering of the BS on the bottom corner:

enter image description here

The laser beams come nowhere the crack seen in this picture, but I have no idea how beam splitters shatter and I know how sensitive interferometers are when it comes to alignment.

Will this shattering/crack cause my laser beam to never truly align or cause drifting of the alignment of the two beams when they recombine? Do I need a new beam splitter?


1 Answer 1


If a piece has chipped off, you should be OK. You might smooth any sharp edges with fine sandpaper.

If there is a crack, you might have trouble in the future. Cracks can grow.

It should not affect alignment, so long as you can fasten it down as usual. But you will find out soon enough if you try it and it doesn't work.

  • 1
    $\begingroup$ (+1) Strain induced birefringence is probably not an issue, though this could be easily checked by putting the beam splitter between cheap crossed sheet polarizers and illuminating with white light through the train. Just like glassblowers test for strain in glass. $\endgroup$
    – Ed V
    Commented Nov 23, 2021 at 23:49

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