If someone asked you to measure a change in distance at about one ten thousandths of the diameter of a proton, you’d probably assume you would need access a high-tech lab. The job is certainly too tight for your cheap Harbor Freight calipers. [Opticsfan], though, has a way to help. You might not be able to get quite that close, but the techniques will allow you to measure a surprisingly small distance.
The technique requires a Fabry Perot cavity, an inexpensive spectrometer, and an online calculator to interpret the data. This type of cavity is two parallel mirrors facing each other with a slight gap between them. Light can only pass through the cavity when it is in resonance with the cavity. These have been around since 1899, so they aren’t that exotic. In fact, they are often used in laser communication systems, according to the post.
Using partially reflective mirrors, the device causes interference fringes. The project requires two half-silvered mirrors, a white light source, some binder clips, and some helping hands. Oh, you also need a spectrometer.
The Spectryx Blue spectrometer mentioned in the post isn’t as expensive as a professional instrument, but it still isn’t a throwaway purchase. We wonder if you could use a homebrew spectrometer and get similar results. Light down at these scales is a strange and wonderful thing.
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