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POP output not showing defocus

  • December 16, 2024
  • 1 reply
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chumphreys

I am running a POP analysis of a system that has a zernike standard phase surface. I am trying to add defocus using this surface and observe it in the POP phase output. I am able to see small magnitudes of defocus but once I try to add 10 waves or more the POP output does not appear to reflect the added defocus. Is this a sampling issue or something else? 

0 waves of defocus

1 wave of defocus

5 waves of defocus

10 waves of defocus

 

Best answer by Jeff.Wilde

As explained in the help documentation, the phase of the beam in POP is measured either relative to a reference plane or to a reference sphere, depending on the phase curvature as determined by a pilot Gaussian beam.

 

In your case, for 0 waves of defocus the POP phase is measured relative to a reference plane:

 

However, for 10 waves of  defocus, the POP phase is computed relative to a reference sphere with the stated radius of curvature:

 

Taking the reference sphere radius into account should yield the proper amount of defocus.  Note that using this reference sphere approach helps significantly with sampling of the wavefront.

You may also want to look at the wavefront map for your system to confirm that the proper amount of defocus is being applied.

Regards,

Jeff

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Jeff.Wilde
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  • December 17, 2024

As explained in the help documentation, the phase of the beam in POP is measured either relative to a reference plane or to a reference sphere, depending on the phase curvature as determined by a pilot Gaussian beam.

 

In your case, for 0 waves of defocus the POP phase is measured relative to a reference plane:

 

However, for 10 waves of  defocus, the POP phase is computed relative to a reference sphere with the stated radius of curvature:

 

Taking the reference sphere radius into account should yield the proper amount of defocus.  Note that using this reference sphere approach helps significantly with sampling of the wavefront.

You may also want to look at the wavefront map for your system to confirm that the proper amount of defocus is being applied.

Regards,

Jeff


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