A dichroic mirror is an interference-based beamsplitter that achieves "transmit short wavelengths, reflect long wavelengths" or "transmit long wavelengths, reflect short wavelengths" at a 45° angle of incidence. It typically features a slope <2% and isolation between transmission and reflection bands ≥OD6. Through precise phase control using dozens of layers of Ta?O?/SiO? or TiO?/SiO? dielectric coatings, it can be customized for any cutoff wavelength between 350 nm and 1600 nm (e.g., 488 nm, 560 nm, 635 nm). The laser damage threshold is ≥5 J/cm2 (ns pulse), with surface flatness of λ/10 @632.8 nm and roughness <0.3 nm RMS. With a thickness of only 0.5–1.1 mm, it is suitable for multi-channel simultaneous acquisition imaging applications such as fluorescence microscopy, flow cytometry, laser combining/splitting, hyperspectral imaging, and Raman confocal systems. It serves as the "core optical switch" in modern multicolor optical systems.