An arrangement in the illumination beam path of a laser scanning microscope, comprising a mirror which can be introduced into the beam path for coupling in at least one additional wavelength, and a method for the operation of a laser scanning microscope with a mirror which can be swiveled in rapidly for coupling at least one additional wavelength into the illumination beam path, wherein the swiveling process is synchronized with the illumination control by a control unit in such a way that at least one additional wavelength is coupled into the illumination beam path when the mirror is swiveled out.