Development of Non-sequential Ray-tracing Software for Cosmic-ray   Telescopes
  We have developed non-sequential ray-tracing software which is aimed to be widely used, along with air- shower simulations, in the design of optical systems for cosmic-ray experiments. The code is based on the ROOT geometry library to provide a non-sequential photon tracking system, which is valuable when simulating refraction and multiple reflections. In addition to the basic ROOT classes, we have implemented new geometry ROOT classes so that users can flexibly define various geometries such as aspherical or Winston-cone type surfaces. We demonstrate the capabilities and performance of the software with examples of optical systems used in current and future experiments. 
Akira Okumura, Masaaki Hayashida, Hideaki Katagiri, Takayuki Saito,   Vladimir Vassiliev
astro-ph.IM