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Question

Beam Profile Analysis using Physical Optics Propagation


pricecj

I would like to use POP to measure the size and profile of a beam as it approaches its focal position, however, I am struggling to configure this correctly. The model is a recreation of an experiment I have setup in the lab as I would like to compare the results. The input beam has a very low divergence value (~0.04 mrads, NA 0.000035), and a single achromat lens is used to focus the beam. The position of the lens relative to the source has been set to give a diameter of  ~ 2 mm at this surface. Using the tutorial https://support.zemax.com/hc/en-us/articles/1500005488601-Using-Physical-Optics-Propagation-POP-Part-1-Inspecting-the-beams I cofnigured the aperture type and POP seetings to create the approprite beam definiton and launch conditions.  I then placed various dummy surfaces throughout the system to assess the beam waist.

 

 

The problem arises when the beam reaches the lens surface (surface 3). No matter how much I change the size of the sampling grids of the previous surfaces (1 and 2), the model returns a non spherical profile, and all subsequent surfaces (4 to 8) have a very small non-gaussian profile.

 

 

 

But then at the focal plane, I get something that looks like this.

 

 

I have a feeling I am not configuring the model correctly; I really need some help! I have attached the Zemax files for clarity. Any assistance with this would be most appreciated :)

Chris

2 replies

Jeff.Wilde
Luminary
Forum|alt.badge.img+3
  • Luminary
  • 505 replies
  • April 17, 2025

@pricecj:

Your starting beam is a Gaussian with a 4 um waist.  At 532 nm, this corresponds to an NA = 0.042.  You then propagate this beam 30 meters to the lens.  When the beam reaches the lens it is a couple of meters in diameter, which looks nothing like your ray trace.  I think you need to modify your starting beam profile and turn off “resampling after refraction” on your surfaces (let Zemax auto sample for you).

Regards,

Jeff


pricecj
  • Author
  • Infrared
  • 5 replies
  • April 28, 2025

Hello Jeff,

Many thanks for your reply. I can now see clearly where I have gone wrong!

Regards

Chris


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