I have a red laser and BS. Can I make MZI at the lab? I heard that is very difficult to achieve the calibration. What is expected to be seen after BS2? A dark spot at centre with fringes around? I searched a video on net but they very unpleasant and in one they said they can not arrange it because the paths difference can not be tuned by hand.


1 Answer 1


Besides the BS you need a few other components:

  • Make sure the BS is at least working at the wavelength of your laser.
  • You need at least 2 mirrors and 2 BS in order to achieve interference:

From Edmund Optics

  • The lens may or may not be necessary,depending on how big your beam is. I would definitely suggest to have at least a few lenses at hand or a beam expander in case your laser beam is too narrow (To be able to observe the fringes "by eye" I recommend ~20-30mm).
  • The mirrors are used to make the optical paths equal. You need to make sure that the optical paths are exactly the same (this is done by making the lasers exactly 90° with each other and measure the propagation distance between BS and mirrors)
  • The sample is not necessary, you can also achieve fringes of the laser itself.
  • The first BS should be preferably 50:50 so you see the power split evenly
  • The second BS is to have the beams overlap before reaching the screen, I forgot if these have to have a specific ratio, I think I used a 10:90

in one they said they can not arrange it because the paths difference can not be tuned by hand.

That's not true. With some elbow grease you can achieve a fair equal-path between the beam splitters, just have a millimeter-range ruler at hand, and preferably use e.g. bore holes in an optical table to get a good reference.

If you have little experience aligning lasers it may take you longer, but it should be possible to make an interferometer "at-home".


The solution Edmund Optics gives is actually rather fancy, you should be able to build the interferometer with less components, although I strongly recommend at least something optics-grade to make your life easier.

  • $\begingroup$ Thanks very much. I don't want a sample. I very perplexed by the intf pattern fringes right on your scheme of MZI. Is this with sample? I thought I would see a black circle on D1 and white on D2 surrounded by citcles of light. $\endgroup$
    – Mercury
    Feb 15 at 12:00
  • $\begingroup$ Sorry what do you mean by elbow grease? $\endgroup$
    – Mercury
    Feb 15 at 12:01
  • $\begingroup$ 1. You should see a black circle with fringes, you are correct. The sample changes the orientation of the fringe pattern. 2. "Elbow grease" sorry this is an americanism, it is meant to mean something that requires a lot of physical effort or labor. I did a "manual" MZI with that setup above and it worked very well, nice visible fringes with 25mm beam but I spent maybe 1 week at the lab measuring the exact positions between mirrors and making the beam travel very straight. $\endgroup$
    – ondas
    Feb 16 at 13:07

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