Michelson Interferometer Comes Home Cheap
We suspect there are three kinds of people in the world. People who have access to a Michelson Interferometer and are glad, those who don’t have one and don’t know what one is, and a very small number of people who want one but don’t have one. But since [Longest Path Search] built one using 3D printing, maybe the third group will dwindle down to nothing.
If you are in the second camp, a Michelson interferometer is a device for measuring very small changes in the length of optical paths (oversimplifying, a distance). It does this by splitting a laser into two parts. One part reflects off a mirror at a fixed distance from the splitter. The other reflects off another, often movable, mirror. The beam splitter also recombines the two beams when they reflect back, producing an interference pattern that varies with differences in the path length between the splitter and the mirror. For example, if the air between the splitter and one mirror changes temperature, the change in the refraction index will cause a minute difference in the beam, which will show up using this instrument.
The device has been used to detect gravitational waves, study the sun and the upper atmosphere, and also helped disprove the theory that light is transmitted through a medium known as luminiferous aether.
The tolerances for such a device are tight, but within the capability of modern 3D printers. The CAD files are online. The key was the mirror mounts, which use springs and thumbscrews. So you do need some hardware and, oh yeah, a laser, although that’s not as hard to obtain as it once was. You obviously can’t 3D print the mirrors or the beam splitter either.
The post claims the device is cheap because the bill of materials was roughly $3, although that didn’t include the beamsplitter, which would bring the cost up to maybe $20. The device, in theory, could detect distance changes as small as one wavelength of the laser, which is around 650nm. Not bad for a few bucks.
Not all Michelsons use lasers. The man behind the Michelson instrument also worked out how to do Fourier analysis with a mechanical computer.