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off-axis parabolic mirror (NSC)


Nanday

I’d like to change a general spherical mirror into a off-axis parabolic mirror to avoid astigmatism. 

In order to do this, I input ‘-1’ as conic 1 parameter as you can see following image.

But It doesn’t work at all…. 

 

Could you help what did I missed?

 

 

Best answer by Allie

Hi @Nanday

Looking at your file, I see the rays are striking your optic at the center of the optic, directly upon the local axis of the object:

 

 

Consider the sag profile of the Standard Lens type, as shown below:

 

 

If we plot this equation for k = 0 and k = -1, then we will see that for your aperture, the sag profiles are essentially the same:

 

 

It is only at large values of “r” that we start to see some deviation, as shown below here:

 

 

It is for this reason that an off-axis mirror is typically used at some point offset from the local axis origin.

In Sequential Mode, we can achieve this through the use of an aperture decenter and/or Coordinate Break surface, as is shown in the sample file C:\...\Zemax\Samples\Short course\Advanced Optical System Design Using OpticStudio\OAP_OSDUZ.zmx.

In Non-Sequential Mode, I would suggest switching to the Off-axis Mirror object type. This object type lets us define the surface sag, as well as the surface offset as discussed in the following forum post:

 

 

Try out that alternative object type and see if you can get the performance you’re after. Let us know if you have any other questions!

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2 replies

Allie
Zemax Staff
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  • Zemax Staff
  • 337 replies
  • Answer
  • June 10, 2022

Hi @Nanday

Looking at your file, I see the rays are striking your optic at the center of the optic, directly upon the local axis of the object:

 

 

Consider the sag profile of the Standard Lens type, as shown below:

 

 

If we plot this equation for k = 0 and k = -1, then we will see that for your aperture, the sag profiles are essentially the same:

 

 

It is only at large values of “r” that we start to see some deviation, as shown below here:

 

 

It is for this reason that an off-axis mirror is typically used at some point offset from the local axis origin.

In Sequential Mode, we can achieve this through the use of an aperture decenter and/or Coordinate Break surface, as is shown in the sample file C:\...\Zemax\Samples\Short course\Advanced Optical System Design Using OpticStudio\OAP_OSDUZ.zmx.

In Non-Sequential Mode, I would suggest switching to the Off-axis Mirror object type. This object type lets us define the surface sag, as well as the surface offset as discussed in the following forum post:

 

 

Try out that alternative object type and see if you can get the performance you’re after. Let us know if you have any other questions!


Nanday
  • Author
  • Single Emitter
  • 1 reply
  • June 18, 2022

Thanks for the thoughtful reply.

As you said, I replaced it with an off-axis mirror.
Still could not overcome the problem of astigmatism.

Can you give me some hints to solve the astigmatism problem?

 

 


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