problem in optimising the beam spot in spectrometer

  • 5 September 2022
  • 1 reply


i am Akshay, new to zemax. I designed a spectrometer with mirror transmission grating and lens system. i could not able to focus the beam spot within airy disk diffraction limit. 

i did optimisation added variables in the merit function editor , given weights changed them accordingly. i have seen some difference but not able to get it within the diffraction limit.


 source as single mode fiber as point source with entrance pupil dia , 0.0042 mm

wavelengths 815,840(central wavelength),860

object distance 0.022 mm calculated for 1/e2 intensity NA at 0.09

parabolic mirror MPD139-M01 - thorlabs

focussing lens AC254 150B - thorlabs

i attached the file here. 

i tried many things but cant figure it out myself , can anyone help me out , i will be grateful 

Thanks indeed





Best answer by Ethan 13 January 2023, 05:26

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Userlevel 3
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Hi @aki_1458,

Apologies for the delayed response to your question. In case it is still relevant or for the benefit of others:

Optimizing an optical system can take practice and know-how. There are many pitfalls a system designer can make, like adding too many variables at once (or adding inconsequential variables), making poor choices on the initial system/components, and not using analysis tools sufficiently to understand where the aberrations in their system come from and how to correct them. There is a good webinar that touches on many points in optimizing your system that might help: Identifying aberrations with OpticStudio features - webinar – Knowledgebase (