Hi,
I just found this forum, and it seemed like the perfect place to ask
about this. I have an older Shack-Harmann WFS from WaveFront
Sciences. I was using it to check colimation for a holography
set-up, and no matter what, the minimum measured astigmatism was
~lambda/10. All other aberations (defocus, coma, spherical) were
~lambda/50. THe RMS wavefront deviation is ~lambda/30, mostly due to astigmatism, it would seem.
After some digging, I found a Blue Sky Collimeter in the back of a
cabinet in the lab, and used this for an independent measure. The
beam *blinks* on and off - so it would seem the phase is very flat.
I tested the calibration of the WFS by placing it several meters from
a pinhole, and measuring the radius of curvature. It was within the
error of my tape measure.
Is there a minimum phase error a WFS, or its software, can measure
correctly? As in, if the error is too small, numerical noise or
something else becomes an issue? Could it be that after all these
years, the hardware no longer matches the calibration file?
Thanks for any feedback, David
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