RMS Wavefront Error from Monte Carlo doesn't match Wavefront map

  • 30 July 2020
  • 2 replies
  • 317 views

Hi all,


I think I'm stuck on a problem of interpretation of results, and maybe someone can illuminate me. After performing a tolerance analysis with RMS wavefront, if I open the MC_XXX.zmx file and compare the results at the Wavefront map, the value shown for RMS Wavefront Error does not match the estimated value at the tolerance summary tab.


Let's take for example MC_Worst, which in my case is run # 254, which has a value of 6.312 waves:



Then, when opening MC_0254.zmx, and going to the Wavefront Map, I get 0.2353 waves, as show in the following screencap:



 


Notice that for the tolerance analysis the TWAV operand is set at 0.6328, and I'm using the same wavelength at the wavefront map.


Is there any conversion between the RMS wavefront of the tolerance analysis and the RMS value from the Wavefront Map? Could it be an incorrect setting of the tolerance analysis?


 I appreciate your comments on this.


Thanks,


José


2 replies

Userlevel 3
Badge +2

Hi Jose,


the discrepancy you are having is because when tolerancing, if the selected criterion is 'RMS Wavefront' the default algorithm to trace rays is the Gaussian Quadrature technique, whereas the Wavefront Map uses a grid to sample the pupil.


You can find a description of this algorithm browsing the help files as such:


The Optimize Tab (sequential ui mode) > Automatic Optimization Group > Optimization Wizard > Pupil Integration Settings > Gaussian Quadrature


This algorithm doesn't account for the effect of vignetting, and therefore, if there are surface apertures in the optical system that vignette enough rays to alter the effective shape of the pupil significantly, GQ should not be used:



What you can do is build a merit function using Rectangular Array algorithm for Pupil Integration:



The Optimize Tab (sequential ui mode) > Automatic Optimization Group > Optimization Wizard > Pupil Integration Settings > Rectangular Array


And then use the Merit Function as your criterion when Tolerancing:



This should give you similar results:



Note that in your MC file, if you use the 'RMS vs Field' tool with 'Gaussian Quadrature' method, the results match the ones obtained in the Tolerancing Summary tab:



Best,


Berta

Hi Berta,


Thank you very much for your help! That solved my issue:



 


Best regards,


José

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