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# What is the best way to model a Gaussian beam?

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Userlevel 6
+2
• Zemax Staff
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It seems like there are a few different ways to model a Gaussian in OpticStudio. What way is best?

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Best answer by Allie 11 February 2019, 18:38

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Userlevel 6
+2

Where possible, a Gaussian beam should be modeled using a ray-based approach. If the system lies within the Rayleigh Length, then the Gaussian beam can be modeled using collimated rays, and if the system lies well outside the Rayleigh Length, the Gaussian beam can be modeled using a point source.

In the intermediate region - or if the beam is nearly collimated over a long propagation distance - the ray-based approached will not be sufficient, and in this case, the Paraxial Gaussian Beam analysis feature should be used. Furthermore, if the beam is brought to an intermediate focus or diffraction effects far from focus are important, then the Physical Optics Propagation analysis feature should be used instead.

Userlevel 1
+2

There are also methods using skew rays which can be used to optimize optical systems or analyze Gaussian beam properties in many situations, including long propagation distances or intermediate focus or even general astigmatism (cylinder lenses not aligned with the x-y axes).  See the Zemax webinar here:

Userlevel 4
+3

Hello, this approach with skew rays seems very powerful. However, how can we define these skew rays in practice ?

Thanks, Cyril

Userlevel 4
+1

Hi Cyril,

Paul Colbourne's webinar has done the community a great service by putting these methods out there. But while the YouTube site contains the presentation, you can get additional information at the Zemax Webinar page here:

https://my.zemax.com/en-US/Knowledge-Base/kb-article/?ka=KA-01772

In addition to the video, the webinar page has the Zip file with included OpticStudio sample files, plus the Paul's article that he references for free download. This way you can get yourself started.

Good luck and have fun!

Userlevel 6
+2

In non-sequential, we have two sources DLL that uses rays to model the propagation of Gaussian beams:

• SkewRaysCircular.DLL: it generates skew rays as mentioned by Paul. This source propagates a circular beam and works for simple astigmaric systems (aligned with the x-y axes). It models the envelope of a gaussian beam.

• GaussianSource.dll: it defines the spatial and angular distribution of rays using the beam waist, the beam position and the M^2 factor.

For more information, check our help file under The Setup Tab > Editors Group (Setup Tab) > Non-sequential Component Editor > Non-sequential Sources > Source DLL.