Paraxial gaussian beam data

  • 14 July 2022
  • 3 replies

My optical setup has fiber laser output which collected and collimated by collimating lens and then focusing lens(Plano convex) . And then, I have system of Galvano mirrors (Maximum scanning angle ±22° ) for 2D scan over square field area. So, I am observing spot diameter for center and corner position of square field area(250*250 mm^2) using feature Paraxial gaussian beam. Here, I am attaching Spot diagram and paraxial gaussian beam data. Please note that, configuration 1 is for spot in center position and configuration 9 is for one the corners position. I am also attaching 3D layout for better visualisations. 

I get same value for laser spot diameter center position as well as corner position of image plane. Theoretically I should get larger value (and non-circular shape) of corner points than center because path length for beam increase for beam as shown in spot diagrams. But paraxial gaussian beam data shows similar value for configuration 1 and 9(in fact for all). I would be grateful if anyone can help me to understand my mistakes.


Best answer by David.Nguyen 14 July 2022, 11:26

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Userlevel 6
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Hi Hina,


I don’t see your images unfortunately (it says “Image could not be loaded”) :(

Without seeing your images, I can point you to this excerpt from the Help File about this analysis feature:

Paraxial Gaussian beams are limited to on-axis simply astigmatic systems


This means that if the beam is not colinear with the optical axis and/or you have elements in your system with an optical power that is not rotationally symmetric or at least aligned with the X and Y axes, this analysis will not work. Which is probably why you are always seeing the same result. It probably ignores your coordinate breaks.

It might sound surprising, but even if you beam is rotationally symmetric, and your optics is rotationally symmetric as well. The simple fact that your beam could hit a lens at an off-axis position creates general astigmatism, which is more complex to handle than simple astigmatism.

I highly recommend this webinar from Paul Colbourne, where he describes a method to trace generally astigmatic Gaussian beams. It will probably not be an easy solution to implement, but it sounds feasible.

Alternatively, you could use a Gaussian apodization and look at the spot diagram.

Perhaps not the answer you were looking for, but hopefully you can make something out of it.

Take care,



Hello David, 

Thank you so much for answering. I will refer this seminar and see if I can find solution. 

Here, I attach again my images. I hope you can see it now. 

Best regards,


Userlevel 2
Badge +2

Thanks for commenting, David. @Hina did this work for you?