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.
From Yashwant Gupta, "Phased Arrays":
"For identical elements, this phased array gives a sensitivity which is n times the sensitivity of a single element, for point source observations. The beam of such a phased array is much narrower than that of the individual elements, as it is the process of adding the voltage signals with different phases from the different elements that produces the narrow beam of the array pattern."
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German Virtual Observatory
hillexed
arcmath