Mie scattering from a single water droplet

  • 18 November 2020
  • 1 reply


I am attempting to model mie scattering for a single water droplet illuminated by a laser beam (monochromatic, collimated, and planar) and see the 'rings' on the detector varying with particle size. There is already a similar post: 

but no solution was reached.

My current setup features a 'source ellipse' as the light source and a single 'Sphere' object as the water droplet with DLL Defined Scattering enabled under the Volume Physics tab. This much I have learned from the Zemax knowledgebase article entitled 'How to simulate atmospheric scattering using a Mie model'. My question now is what values for density and mean path should I enter in the MIE.DLL section under the Volume Physics tab?

Suppose I start with a 10 micron diameter water droplet and I place the detector 500um (0.5mm) away from it, what density and mean path values correspond? Or is there a better approach?

Thank you in advance.


Best answer by Christophe.Weisse 23 January 2023, 18:07

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I was about to open a new thread, and I then came across this unanswered one.

The main difference here is that OpticStudio applies the Mie Scattering model considering the Mean Free Path or the density of the particles inside a (way) larger volume. The ray can then be scattered several times, depending on the probability to “hit” another particle.

To avoid this, the main “trick” here is to actually select the scattering option of the source to “Once” instead of “Many” in the source properties:

And then you can easily spot the typical pattern (rings) on a cross-section, using a logarithmic scale:


I’ve attached the design file for convenience.

I hope this helps,