We will put the glass spheres in a cup with metallic walls. The bottom of the cup is realized as a circular interface, the side walls are made using an open cylinder. Open the list of geometric objects by pressing the Objects button in the main window of SPRAY. Create a circular interface (object type 'Circle') with name 'Bottom' and the following coordinates:
Note that the normal vector points downward. Now open the list of interfaces and drag the interface 'Air-metal-air' to the label 'Interface: None' and drop it there. If the dialog now looks like the following, press OK to close it:
Now create an object of type 'Cylinder (open)', name it 'Side' and enter the following settings (do not forget to assign the interface by Drag&Drop from the list of interfaces):
The illumination of the sample cup is done from above, using a light source of type 'Circular light source' (I named it 'Lamp') with these coordinates and assignments:
Note that the light source is not absorbing. We will finally put a huge rectangular detector above the present setup which will collect all rays that are reflected. Create an object of type 'Rectangular detector' and enter the these numbers:
In the section about basic skills you have learned how to define 'rendered views' which should be used to check the setup. Create one with the following parameters:
Then run the simulation by pressing the Simulation button in the main window. The simulation should not take very long because there is just a simple reflection of the rays at the bottom interface. Since silver is a noble metal its reflectivity in the infrared is very high. Open the detector object in the list of objects and use the View data command to display the spectrum. I obtained the following spectrum which confirms the expected result:
What is left to do is to add the scattering glass spheres to the system. This requires some further actions. First we need another interface which defines the transition from air (filled with no scatterers) to air filled with our scattering glass spheres. To do this open the list of interface again and create another layer stack, named 'Air - glass spheres'. Open the layer stack definition:
Since the glass spheres are embedded in air, there is no real physical transition from one material to another, and vacuum is used on both sides of the interface. However, crossing the interface means to enter a scattering medium. You can set the scatterers on both sides of the interface by using the Properties|scatterers command. The following dialog opens:
You can assign scatterers to the top and bottom halfspace by Drag&Drop from the list of scatterers. In this case, we need the following assignment:
Also the interface 'Air-metal-air' has to know which scatterers are on which side. Open this interface from the list of interfaces, use the Properties|scatterers command and do the same assignment as above:
This means that there are scattering glass spheres inside the cylinder and no scattering objects outside.
The very last action is to introduce another circular interface at the top of the sample cup which defines where in space the scattering medium begins. Go to the list of objects, create a new object of type 'Circle' and assign the interface 'Air - glass spheres' to it. The geometrical parameters are the following:
These modifications should be checked in the view object. Open it and repaint the image with Draw. Sending some test rays clearly shows the diffuse light scattering now:
That's it! We are now ready to compute the first diffuse reflectance spectrum of scattering glass spheres in a metallic cup. The current configuration has been saved in the file tu1_ex2_3.s99.