Optical metrics: How do you convert spotsize @FWHM to RMS wavefront error?

Question

FWHM = full with at half-maximum
RMS = root mean squared

Assuming 1 wavelength. Or if you can go in the reverse, I could figure it out backwards. Your help is much appreciated.

Thanks injanier, that's a good response because I can compute strehl from the ratio of my spot size height to that from a diffraction limited optic. Then I can set this strehl equal to the rms strehl formula you provided. I will leave the question open a little longer just to see if there are any more direct approaches. I would prefer to get a formula involving FWHM, but yours should work. Thanks Angie for your response too, but my paying for your physics classes might not be the most expedient solution.

Answer 1

I don't know about FWHM spot size, but Strehl ratio and RMS wavefront error are related by r = 1 - 4 (πw)^2, where r is Strehl ratio and w is wavefront error. This relationship breaks down as optical quality falls below diffraction limited (r=.8).

Answer 2

Uhh, sorry I didn't take physics in high school!! I took Chemistry