Introduction: DIY LEGO Light Interferometer

About: Science geek

Interferometers are investigative tools used in many fields of science and engineering. They are called interferometers because they work by merging two or more sources of light to create an interference pattern, which can be measured and analyzed; hence 'Interfere-o-meter'.

Today i will make an interferometer using lego and some other common materials.

This is a very cool experiment and is used in many fields in science such as the LIGO.

Once the set up is compelete, you can observe the interference pattern formed by the interference of two laser beams.


  1. LEGOs
  2. 2 plane mirrors
  3. beam splitter cuber(i have used a microscope glass slide)
  4. LASER
  5. rubber bands to hold the LASER
  6. magnifying glass

Step 1: Make a Base Plate (skip If You Already Have One)

If you already have a baseplate large enough to fit all the components, then skip this step.

I did not have a baseplate so I had to make one using separate lego plates and lego blocks

Step 2: Build a U-shaped Holder for the Laser

Use a long lego block and 3-4 L shaped legos(as shown in the picture), to create a holder where you can place the laser and hold it firmly with rubber bands. Don't leave any extra space between the laser and lego fill all gaps(if any) between them with paper, and make sure the laser does not bulge

Make sure you can access the on-off buttons on the laser while it is held by the rubber bands, you don't want to waste your battery.

Step 3: Make a Stand for Mirrors

  1. use some 1x6 lego bricks to make a stand with 2 L shaped bricks on opposite sides that will hold the mirros from the front, make 2 of these for 2 mirrors(refer to the image)
  2. place a 2x2 lego piece that has a rotatable center on the path of the laser beam.
  3. place the mirrors on 2 sides of the rotatable lego piece, as it is in the picture.both mirrors should be placed on equal distance from it.

Step 4: Make a Beam Splitter

  1. take a 2x8 lat lego plate and attach 2 1x22 bricks on either side as it is in the picture.
  2. place the glass slide between them.

Beam splitter is ready, now just attach it to the rotatable piece we added earlier and refer to he image for its correct orientation.

Step 5: TEST IT !!!

Now turn on the laser and move the laser/beam splitter till the beam passes through the beam splitter.

after the beam is split they should go towards the mirrors and get reflected.

After being reflected they should again meet at the beam splitter and go towards the same direction(as in the picture)

COLOR CODING(for the picture);

RED : beam from the laser before passing through the splitter

BLUE : beams after being split from the beam splitter, and going towards the mirrors.

BLACK : beams after being reflected from the mirrors and moving toward the splitter

GREEN : reflected(black) beams after meeting and merging at the beam splitter.

If you are getting a similar result, the setup is working fine and now all you need to do is move the mirrors/beam splitter slightly to make the (green beams) overlap eachother to for an interference pattern.

Step 6: Magnifiy the Pattern

Once you have adjusted the mirrors and the beamsplitter, to make both beams overlap each other, you need to magnify them to make he patterns observable.

To do this, you need to put a magnifying glass if the path of the beams that are coming out from the splitter.

But, as I broke my magnifying glass, i had to use an alternative. So I bought another laser pointer and salvaged its lens, made a holder from lego and put it in the path of the beams.


Turn of all the lights, and turn on he laser.

IF everything's working as it should. and the beams are overlaping and magnified, you should be able to see this type of pattern.

these horizontal stripe pattern is due to the interference between the waves of two beams of light.