| 摘要 |
A polygonal mirror and a light scanning unit are provided to uniformly form a latent image on an exposure material regardless of the wavelength and polarization properties of a light source and the incident angle of light by using the polygonal mirror. A polygonal mirror includes a main body(11) and first to third dielectric layers(13,15,17). The main body includes plural reflective surfaces(11a) for reflecting incident beams. The dielectric layers are sequentially formed on the reflective surface. The second dielectric layer is made of a material selected from the group consisting of TiO2, Ta2O5, and ZrO2. The thickness of the second dielectric layer lies between 0.23lambda and 0.35lambda for TiO2. The thickness of the second dielectric layer lies between 0.32lambda and 0.48lambda for Ta2O5. The thickness of the second dielectric layer lies between 0.30lambda and 0.46lambda for ZrO2, wherein lambda is the wavelength of the light incident on the reflective surface.
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