The laser scanning microscope uses a point light source to illuminate the specimen, forming a small, well-defined spot on the focal plane. The fluorescent light emitted by this spot is collected by the objective lens and sent back to the beam splitter composed of a two-way color mirror along the original irradiation light path. . The laser scanning microscop beam splitter sends the fluorescence directly to the detector. There is a pinhole in front of the light source and the detector, which are called illumination pinhole and detection pinhole respectively.