The design of a single heater element is shown in one_lamp.zmx, which is included in the attached zip archive on the last page of this article.

The mirrors were entered using ZEMAX's built-in TOROIDAL SURFACE object. This is a parametric object, and it uses facets only for drawing on screen and to provide an initial guess for the ray-object intersection point. For rendering purposes, I used a large number of drawing facets (400) but this can easily be set much smaller (10 is sufficient). Remember that the toroidal surface is smooth, and facets are only used for drawing purposes!

The sides of the parabolic mirrors are modelled using RECTANGULAR SURFACE objects. The sources are modelled as SOURCE FILAMENT objects. Finally, the glass tube was modelled using two CYLINDER VOLUME objects, one inside the other. The outer cylinder is made of fused silica, and the inner is made of air. The source filament is then placed inside of the air cylinder.

Here is a cross-section of the lamp:

and here is a fully rendered image:

This unit was then copied and pasted five times, and positioned relative to a dummy object to get the orientation correct. Detector objects were entered to model the susceptor. Finally the whole assembly was placed inside the external oven assembly:

As the above plot shows, rays from a lamp on the right-hand side may find their ways to the left-hand side of the structure. Therefore, the heater is represented entirely, rather than as a half structure only. For symmetry reasons it is sufficient, nevertheless, to have SOURCE FILAMENT objects only on the right-hand side and to use empty glass tubes on the left hand side. To ensure automatic symmetry of the structure in the course of optimisation, the left-hand side is entirely represented by PICK-UP SOLVES mirroring the right-hand side, so that the optimisation parameters only refer to the surfaces on the right-hand side.