Just like coatings, scattering profiles can be selected for each Coating/Scatter Group on a particular object.  In the current example, re-open the Object Properties dialog for the Rectangular Volume.  Underneath the Coating/Scattering tab, make sure to re-select the 1, Front Face as the “Coating/Scatter Group.” 

There are various built-in scattering profiles in ZEMAX, one of which is Lambertian.  By default, “No Scattering” is selected.  Once the scattering is changed to “Lambertian,” there are two essential data entry fields which become activated: Scatter Fraction and Number of Rays.  The fraction must be between zero (no rays will be scattered) and 1.0 (every ray will be scattered).  How ZEMAX treats these values depends upon whether or not Ray Splitting is turned on (via each specific analysis feature).  For a complete discussion, please refer to the “Scattering” section in Chapter 12 of the ZEMAX User’s Guide.

For the current example, set the scattering to Lambertian and the Scatter Fraction and Number of Rays to 0.8 and 5 respectively.  Therefore, when splitting is turned on, then the scattered energy will be evenly divided amongst the five scattered rays.  The specular ray, on the other hand, will receive a fraction of the total reflected/scattered energy equal to 1.0 – Scatter Fraction.  In this case, the specular ray will receive 0.2W.



Select “OK” to make the applied changes.

In order to verify the changes made to the front face of the Rectangular Volume, choose Fletch Rays, Split Rays, Scatter Rays, and Use Polarization in the settings of the NSC 3D Layout.  Note that the initial source ray is scattered (with Lambertian probability) into 5 rays, for a total of 6 rays reaching the detector.



And, if we perform yet another Monte Carlo Ray Trace, the total power of these rays (provided that all 5 scattered rays hit the detector) is equivalent to 0.6 Watts, or 60% of the initial power.



And, tracing 2.5 million rays and increasing the detector resolution, we can observe that the highest radiant intensity is at normal incidence, which corresponds to the specular, reflected portion of the energy:



So, we have easily created a partially reflective scattering surface in ZEMAX.  The tools and concepts used in this example may be applied to much more complex systems, but the basis and fundamental approach to applying coatings and scattering profiles remains the same.