Now we’ll add some objects to the TIR model to make it an FTIR model.  You remember that in order to “frustrate” TIR, we need to have another high-index (silica) object brought into very close proximity to the first silica object.

To make the bottom slab, simply select the top slab (do this by clicking on Object 1 and dragging down and then dragging back up until the entire Object 1 row is selected), hit CTRL-C, click on Surface 2 (that’s where we want the bottom slab to go), and then hit CTRL-V.  We need to make a few adjustments now.  Change the comment of our new Surface 2 to “bottom slab” and set the Y Position value to -50.  Since the y-height of each slab is 50mm, and the center-to-center spacing is now 50mm, they will now be in direct contact with one another at their edges.  The NSC Editor should look like this:

Now we want to add a detector inside this bottom slab.  To do this, select the detector object (It should now be numbered Object 4), and copy and paste it right below (same way as before) so that the new detector copy is Object 5.  Change the “Comment” of this new detector to “bottom slab det” and then change the “Ref Object” to “2”.  Here is what the NSC Editor should look like at this point:

And here is what the layout should look like:

Because the two slabs are in direct contact, the interface has the same refractive index on either side, as hence no reflection occurs.  Our next step will be to introduce a small airgap between the two slabs in order to model FTIR.