A homogeneous illumination of a microscope requires a homogeneous intensity distribution in the field plane and in the pupil plane. An inhomogeneity in the pupil gives rise to a distortion in the image. This distortion is more clearly seen in defocused image planes and is commonly misinterpreted as classical aberration. An inhomogeneous intensity distribution in the field plane causes for example a line thickness variation of an imaged structure.
In classical microscopy which operates with classical light sources, for example spiral-wound filaments, the task of designing a homogenised illumination can be solved using geometrical optics. Using instead of an incoherent a partial coherent light source may lead to interferences in the pupil and in the field plane which represent the major problem of such illumination systems.
We present simulated results concerning the propagation of partial coherent light. The lateral and temporal coherence of a multimode laser was determined experimentally. With these results simulations were done using partial coherent beams. The considered optical components include lenslet arrays and diffractive optical elements.