A method for illuminating a sample slice uses a light beam or a light sheet during single plane illumination microscopy (SPIM). The light beam or light sheet is deflected by an angle mirror having a first and second reflective surface reflecting a first and second portion of the light beam or light sheet, respectively, whereby the first and second portions of the light beam or light sheet spatially overlap one another after the deflecting. Alternatively, the light beam or light sheet is refracted by a refractive optical component comprising a first and second refractor surface refracting a first portion of the light beam or light sheet, respectively, whereby the first and second portions of the light beam or light sheet spatially overlap one another after the refracting.