| 摘要 |
PURPOSE:To improve the resolution of the beam scanning optical device by setting conjugation deviation in a width-scanning direction with the depth of focus of a cylindrical lens which forms a focal line. CONSTITUTION:This device has a light source 11, a rotary polygon mirror 15 which reflects and deflects a beam toward a scanned surface by the rotation of plural reflecting surfaces, 1st optical systems 12-14 which form a line image of the beam from the light source 11 on a reflecting surface 15a of the rotary polygon mirror, and 2nd optical systems 16 and 17 which image the line image, formed on the reflecting surface 15a, on the scanned surface in a spot shape and correct the surface tilt of the reflecting surface 15a by making the positions of the reflecting surface 15a and scanned surface optically conjugate about a subscanning surface. The 1st optical systems 12-14 satisfy NA<=(phi/2ky)<1/2> and 0.6<=k (constant) <=1.0, where NA is numerical aperture, phi is the spot diameter of the beam on the scanning surface, and (y) is a half of a scanning range. Consequently, the divergence of the beam spot in the subscanning direction can be suppressed within an extremely narrow constant range. |
