That requires the next phase I'm waiting on: nm-scale lithographic printing on silicon.
PLL with a small number of feedback markers and high quality OCXO might suffice?
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The tricky bit I guess is that you need a high angular feedback frequency to compensate for mechanical instability.
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I.e. no matter how good your PLL is, one pulse per revolution isn't enough for nm-scale accuracy.
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To avoid need for precise even spacing of marks, could you have one primary pulse per rev and many minor ones...
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...and measure timing between each one (average over many revs) before start to get phase offsets for each to feed into PLL?
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Depends on whether you need dimensional accuracy or just track-to-track repeatability I guess. That sounds like it'd work for the latter.
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I think it would work for either, no? Once you correct for phases of minor marks, everything is stable relative to the primary one.
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I think the issue is you can't easily correct for the spindle not being perfectly centered and the like. That'll introduce consistent error.
End of conversation
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