A fluorescence microscope instrument comprising: - a light source providing light to be directed to a sample; - a detector detecting fluorescence light emitted out of the sample; - an objective focusing the light from the light source into a focal area within the sample and collecting the fluorescence light emitted out of the focal area to be detected by the detector; and - a beam path separator arranged in a beam path of the light from the light source between the light source and the objective and in a beam path of the fluorescence light between the objective and the detector and separating the beam path of the fluorescence light from the beam path of the light from the light source, - wherein wavelengths of the light to be directed to the sample and of the light to be detected by the detector fall into a range of wavelengths extending from a low end wavelength over at least 20 % of the low end wavelength, characterized in - that the beam path separator is configured to be periodically transferred between - a first state in which the beam path separator is transparent by at least 75 % for light of any wavelength falling into the range of wavelengths and coming along the beam path of the light from the light source to the sample, and - a second state in which the beam path separator is transparent by at least 75 % for light of any wavelength falling into the range of wavelengths and coming along the beam path of the fluorescence light from the sample to the detector within the sum of the travel time of the light of the light source from the beam path separator to the sample and the travel time of the fluorescence light from the sample to the beam path separator; and - that the beam path separator comprises two polarization beam splitters (13, 14) and a birefringent electro-optical element located between the two polarization beam splitters (13, 14), the birefringent electro-optical element being configured to rotate a polarization direction differently in the first and second states of the beam path separator. - a light source providing light to be directed to a sample; - a detector detecting fluorescence light emitted out of the sample; - an objective focusing the light from the light source into a focal area within the sample and collecting the fluorescence light emitted out of the focal area to be detected by the detector; and - a beam path separator arranged in a beam path of the light from the light source between the light source and the objective and in a beam path of the fluorescence light between the objective and the detector and separating the beam path of the fluorescence light from the beam path of the light from the light source, - wherein wavelengths of the light to be directed to the sample and of the light to be detected by the detector fall into a range of wavelengths extending from a low end wavelength over at least 20 % of the low end wavelength, - that the beam path separator is configured to be periodically transferred between - a first state in which the beam path separator is transparent by at least 75 % for light of any wavelength falling into the range of wavelengths and coming along the beam path of the light from the light source to the sample, and - a second state in which the beam path separator is transparent by at least 75 % for light of any wavelength falling into the range of wavelengths and coming along the beam path of the fluorescence light from the sample to the detector - a first state in which the beam path separator is transparent by at least 75 % for light of any wavelength falling into the range of wavelengths and coming along the beam path of the light from the light source to the sample, and - a second state in which the beam path separator is transparent by at least 75 % for light of any wavelength falling into the range of wavelengths and coming along the beam path of the fluorescence light from the sample to the detector - that the beam path separator comprises two polarization beam splitters (13, 14) and a birefringent electro-optical element located between the two polarization beam splitters (13, 14), the birefringent electro-optical element being configured to rotate a polarization direction differently in the first and second states of the beam path separator.