Methods for determining the blackbody radiation and photon rate for an infrared telescopes

The evaluation of background radiation for an infrared instrument is critical to determining the ability to detect faint sources and signals. This background is often limited by the thermal emission of the telescope itself. However, software tools to make this assessment are limited. Here, a method is described that uses a conventional non-sequential ray tracer enhanced to efficiently compute background radiation. The methods include using tessellation to efficiently trace emission and comparison with analytical expressions. The method is used in a case study to evaluate the blackbody radiation intensity for both an on-axis telescope and an off-axis telescope.