The invention relates to an illumination apparatus for a microscope, a microscope and a method for operating the illumination apparatus. The illumination apparatus has a sample space for holding a sample that is to be illuminated, and at least one laser light source. An objective for the directional emission of laser radiation of a first wavelength along a first optical axis that is directed into the sample space, and with a cover of the sample space by which the sample space is delimited at least on one of its sides. The cover further has a layer that is either impenetrable for the laser radiation over a blocking angle range of the illumination angle and is transmissive for radiation of a second wavelength over a transmitted light angle range, or has a controllable layer that, in a first control state, is transparent for radiation of the second wavelength and, in a second control state, is impenetrable for the laser radiation of the first wavelength.