POLYGON MIRROR AND LASER SCANNING UNIT HAVING THE SAME AND IMAGE FORMING APPARATUS HAVING THE SAME

摘要

A polygon mirror and a laser scanning unit and an image forming apparatus having the same are provided to maintain constant reflectivity at various wavelength bands. A reflection plane reflects a laser beam. A first(20), a second and a third dielectric layers(30) are stacked on the reflection plane. The second dielectric layer is TiO2. The first dielectric layer and the third dielectric layer are SiO2. If the wavelength of the light incident on the reflection plane is lambda, the thickness of the first dielectric layer is 0.91 x lambda and the thickness of the second dielectric layer is 0.36 x lambda and the thickness of the third dielectric layer (40)is 0.25 x lambda.