absorptive and scattering surfaces in NSC

  • 29 December 2019
  • 7 replies
  • 1221 views

ABg scattering seems to describe only scattered rays on "reflective" surfaces in zemax non-sequential mode. Is there an easy way to model a surface that scatters only a fraction of the incident radiation. Any ABg model I apply to a surface seems to include a large specular component I can't seem to control.

 

7 replies

Userlevel 7
Badge +3
Hi Jeff,



There are two separate things going on here that you need to distinguish. First, surfaces can only be MIRROR or ABSORB. If you want to see reflection and transmission, use a volume (3D) object like a Rectangular Volume, with a real (non-idealized) material.



Next, ABg scattering encodes the specular component directly, so you don't have separate control of it. For a given set of A, B and g parameters, the specular component is just A/B. This comes from the definition of the BSDF:



BSDF(x)=A/(B+|x|^g)



For the specular ray, x=0, and so the BSDF is just A/B.
Thanks Mark,

What I am trying to do (and maybe I must create a coating to do this on a volume component) is create a surface that has a large absorption and a defined BSDF (say by ABg model). I'm trying to model some of the modern optical black coatings that can absorb more than 99% of the incident radiation (over most incidence angles) with a small residual scatter of the remaining energy. I've tried adjusting downward the A coef in ABg model but the zemax TIS ray energy normalization seems to undue my attempt to introduce absorption this way...? Thanks for your help. -- Jeff

Hello Jeff!

I know it's been about a year since your post but I'm also interested in modelling a similar optical black coating on a baffle for a telescope. 

Did you get your model to work?


Thanks,


André

Userlevel 5
Badge +2

Hi Andre,


Thanks for your question here!


If you want to model black painted surfaces you need to use a coating. You can choose a coating from our library, or you can create a new one. If you have no data available, you will need to make an estimation as best as you can. You can use MIRROR material, so that light reflects from it, and then you can use a coating to define the reflectivity. The easiest solution would be to use the IDEAL coating with a defined reflectivity and loss. The syntax for this is the following (anything that is not transmitted or reflected, is absorbed):



IDEAL Transmission Reflection TIR

If you need a more complex model with wavelength or angle of incidence dependent response, you can define a TABLE coating.


I would suggest to check out these knowledgebase articles about how to define and apply coatings:


How to define metal materials in OpticStudio · MyZemax


How to model a dichroic beam splitter · MyZemax


How to model a partially reflective and partially scattering surface · MyZemax


How to add coatings and scattering functions to Non-Sequential objects · MyZemax


If you have any further questions, please let us know and we will be happy to help.


Best,

Csilla


 


 

Hello Csilla,


Thank you, that's exactly what I was looking for!

Just for future reference, I'm trying to achieve a behaviour similar to the image below.



If I correctly understood the references you posted, I need to create a baffle with a mirror material, create and add the following ideal coating:

IDEAL BaffleCoating 0 0.05


And then apply a Lambertian scatter model with a scatter fraction of 0.32 (32% of the reflected 5% to achieve the 1.6% shown in the image).


Best regards,

André Santos

Userlevel 6
Badge +2

Hi Andre


Yes correct. You can use an ideal coating I.95 on a mirror. 5% will be reflected and the rest absorbed.


Then as you said, you can use the scatter fraction.


So 5% x Scatter Fraction = 0.32 = 1.6% will be scattered


And 5% x (1 - Scatter Fraction) = 3.4% in the specular direction.


Sandrine

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ABg scattering seems to describe only scattered rays on "reflective" surfaces in zemax non-sequential mode. Is there an easy way to model a surface that scatters only a fraction of the incident radiation. Any ABg model I apply to a surface seems to include a large specular component I can't seem to control.

 

I face a similar problem as Jeff Kuhn did about 4 years ago, but did not find a solution in the many replies to the post. I’m a beginner trying to simulate an integrating sphere, taking off from the very simple sample file “Integrating Sphere.zmx” in “Zemax\Samples\Non-sequential\Miscellaneous”. My aim is to model the sphere efficiency with weakly absorbing lambertian scattering surface and I tried to apply a coating to the sphere object with an IDEAL coating “IDEAL R95 0.05 0.95” combined with Zemax’s standard “Lambertian” scatter model which should give a drastic reduction of the efficiency compared to a 100% reflecting coating due to the many scattering events taking place inside sphere, but this does not happen. Is my problem perhaps  (as somebody suggested) related to to the sphere being modelled as just a surface instead of a solid object?

Henrik Fodgaard

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