From Looking Glass Universe.

This video was supported by Screen Australia and Google through the Skip Ahead initiative.

Part 1 is here: https://youtu.be/muoIG732fQA?si=_vFy9siMqkOdO1xV

f you want to do this experiment at home, you can! It’s very simple.
All you’ll need is:
– a weak red laser pointer (the type in cat toys are generally safe)
– polarizing film or polarizing filter. If you have polaroid glasses or certain camera ND filters you may already have this. Otherwise it’s available on amazon
– half waveplate (the plastic thing) is this one: https://www.edmundoptics.co.uk/f/polymer-retarder-film/14827/ (λ/2 Retarder Film (WP280))
– You don’t need calcite, but if you want to play with it, you can find it on etsy usually. Look for a sample that’s exceptionally clear