An interferometer is a really cool laser experiment you can do at the bench 💪🏼😃
You need a laser diode with a built in photo diode sensor - not all of them have it. Keep the power low, and safe. I chose the ADL65052.
(Laser diodes are NOT like your common LED so if you’ve never played with them before, start with that)
Then build a transimpedance amplifier (a current to voltage amp), connect the output to an oscilloscope and here’s what happens:
The light can be reflected back into the laser, causing constructive and destructive interference. The sensor diode sees this as varying light depending on the distance to the reflector.
It’s REALLY sensitive, it’ll pick up vibrations of the surface of my bench 😳
It’s a well described experiment, there’s a whole Wikipedia article on the principle. The physics behind it is quite sofisticated though - so it’s a neat experiment to replicate 🤓