It has been several months of assembling and tinkering and troubleshooting to get here, but my bath interferometer is finally working! Now I can feed these images of concentric circles into software and analyze the shape of my mirror down to tens of nanometers!

These pictures show a laser beam, split in two by a beam splitter cube, interfering with itself. The dark zones show regions where one beam travelled an integer plus a half number of wavelengths farther then the other beam, so when they add back together they're out of phase and cancel out. A linear polarizing filter on my camera I got helps equalize the brightnesses and make the pattern clearer. The resulting pattern can be interpreted almost like a topographic map of the mirror, where a single ring is all at the same "height" from my 3D printed testing apparatus.

#diy #interferometry #hillescopemaking