Efficient simulation of autofluorescence effects in microscopic lenses

The use of fluorescence in microscopy is a well known technology today. Due to the autofluorescence of the materials of the optical system components, the contrast of the images is degraded. The calculation of autofluorescense usually is performed by brute force methods as volume scattering. The efficiency of calculations in this case is extremely low and a huge number of rays must be calculated. In stray light calculations the concept of important sampling is used to reduce computational effort. The idea is to calculate only rays, which have the chance to reach the target surface. The fluorescence conversion can be considered to be a scatter process and therefore a modification of this idea is used here. The reduction factor is calculated by simply comparing in every z-plane of the lenses the size of the illuminated phase space domain with the corresponding acceptance domain. The boundaries of the domains are determined by simple tracing of the limiting rays of the light cone of the source as well as the pixel area under consideration. The small overlap of both domains can be estimated by geometrical considerations. The correct photometric scaling and the discretization of the volumes must be performed properly. Some necessary approximations produce negligible errors. The improvement in run time is in the range of 10 4. It is shown with some practical examples of microscopic lenses, that the results are comparable with conventional methods. The limitations and the consequences for questions of the lens design are discussed.