[Webinar] Using Skew Rays to Model Laser Beams [Q&A]

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This thread is dedicated to the upcoming webinar: Using Skew Rays to Model Laser Beams. Any questions received during the webinar will be responded to as a reply on this thread. Feel free to post your own questions! The speaker will be notified and will respond as long as the thread is still open.

Be sure to subscribe to this thread if you want to see additional discussion regarding this webinar topic. The thread will be open to new replies until Friday, April 22nd. 


Webinar details

Register here: [The webinar has concluded.]

Date: Thursday, April 14th. 

Time: 6:00 - 6:35 AM PDT, and 11:00 - 11:35 AM PDT

Presenter: Paul Colbourne, Senior Optical Designer at Lumentum


In this webinar, Lumentum’s Paul Colbourne will describe how to use skew rays to model Gaussian beam propagation in OpticStudio. Skew rays are an efficient and accurate representation of Gaussian beams and can be used to quickly optimize for best focus or to minimize aberrations. Paul will demonstrate how to set up User-Defined Surfaces to generate skew rays, how to view circular Gaussian beams in 3D layout diagrams, and how to optimize systems with circular Gaussian beams. In addition, Paul will explain general astigmatism, and how to calculate the properties of a generally astigmatic Gaussian beam in OpticStudio using a ZPL macro. Paul will also show how to use a merit function macro to optimize systems with elliptical or generally astigmatic Gaussian beams.


Allie 1 year ago

Watch the recording!

A recording of this webinar is available here: On-demand Webinar: Using Skew Rays to Model Laser Beams

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Hi Paul,

Thanks again for this talk - I’ve found your tools to be massively useful so far.

When using us_gskew.dll, what is the significance of the aperture definition? I see that you’re using an Object Space NA of 0.3 - making this NA faster seems to increase the offset produced by the .dll, and likewise making it slower reduces the offset. Is there a “correct” setting of Object Space NA, or it situation-dependent?

Thanks again,


Hi Kaia,

Glad you are finding the tools useful.  When using us_gskew.dll, the “correct” value of Object Space NA depends on what you are doing, but could be one that produces the same divergence as the Gaussian beam you are modeling, for example a value of (wavelength)/(pi)/(waist radius) would produce rays with a maximum divergence equal to the 1/e^2 beam divergence. But you may want to analyze with rays further out than the 1/e^2 point to ensure that the optics have low aberration out to the edge of the beam.  What I might typically do is set the Object Space NA to 1.3*(1/e^2 divergence) and use Gaussian apodization with an apodization factor of 1.69, then the launched rays are fairly representative of where the optical power is through the system.  Remember that what the aperture setting does is define which rays are used to optimize and analyze your system.

In the example file, I used a high NA so that the beam width was exaggerated on the layout diagram, so that the Gaussian beam shape was clearly visible.  The high NA has no real design or analysis purpose in that file. 

Paul C.

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Hi everyone,

This thread is now closed. Thank you so much for submitting your questions. And a special thank you to @PaulC for a great webinar and discussion!

If you’re interested in learning more about how OpticStudio handles laser beam propagation in general, check out our tutorials on the topic:

If you have any other questions about this topic, feel free to submit them to our general discussion forum here: Got a question? | Zemax Community