Differential ray tracing for exact radiometric calculations

One of the main tasks of ray tracing is to compute the radiometric performance of an optical system, such as the irradiance distribution on the detector plane. For this end, conventional ray tracers send rays through the system in a stochastic manner. A large number of rays and long computation times are needed to achieve sufficiently accurate results. Differential ray tracing tackles radiometry in a different way, tracing ray bundles with an infinitesimal angular spread. These are emitted from a point source and then propagated through the optical system. The irradiance on any point of the detector plane is obtained exactly by summing the contributions of all ray paths that end there. The differential information contained in a ray bundle can also be used to move it from its original hit point to any other accessible point on the detector, thus allowing for exact irradiance calculations with arbitrary spatial resolution. If the number of light paths is not too large, the suggested method is very efficient. The talk presents the generalization of the method to extended sources, discusses intrinsic limitations and compares its results with calculations from standard ray tracers.