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Optical path length between a flat and a tilted surface, odd behaviour.

  • October 22, 2022
  • 1 reply
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Any ideas why PLEN would not give you the correct optical path length for Py 1 and -1 between a stop and a tilted on X diffraction grating with a period matching the tilt?

 

Best answer by Berta.Bernad

Hello,

The reason is not working as expected is the Diffraction Grating itself. This surface imparts a phase change linearly across the profile of the surface, so when rays pass through the grating, the path length is compensated for the total optical path. 
 
So, you'd want to define a dummy surface with the same material as your grating substrate to be coincident with this diffraction surface. That way, the phase change from the grating is not affecting your PLEN operand with which you are trying to determine physical distance with, and you can use it to this dummy surface to get the geometric paths.
 

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Berta.Bernad
Zemax Staff
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Hello,

The reason is not working as expected is the Diffraction Grating itself. This surface imparts a phase change linearly across the profile of the surface, so when rays pass through the grating, the path length is compensated for the total optical path. 
 
So, you'd want to define a dummy surface with the same material as your grating substrate to be coincident with this diffraction surface. That way, the phase change from the grating is not affecting your PLEN operand with which you are trying to determine physical distance with, and you can use it to this dummy surface to get the geometric paths.
 


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