| 摘要 |
PURPOSE:To obtain an equal scanning speed even with a rotary polygonal mirror of a fewer number of faces by providing plural reflecting faces formed with reflection type diffraction gratings in the direction parallel with a revolving shaft to the circum ference of the revolving shaft. CONSTITUTION:The incident angle of parallel luminous fluxes to the diffraction grating 101 is designated as alpha, the angle of diffraction as beta, the angle between an incident ray 102 and a diffracted ray 103 as 2phi, the angle between a central line 104 bisecting the incident ray and the diffracted ray and the normal 105 of the diffraction grating as theta, the wavelength of the rays as lambda, the inter-grating spacing of the diffraction grating as (e), and the order of diffraction as (m), then phi is given by the equation I. lambda is constant and the light rays of respective orders m=1, 2... are simultaneously deflected by the corresponding phi according to the rotation (i.e., the change of theta) of the diffraction grating by the equation I. Namely, the diffraction grating which swivels in the region of the certain angle phi receive the diffracted light rays of different orders among a series of rotations of theta. Such diffraction gratings are formed on the side faces of the rotary polygonal mirror, by which plural times of the scanning are enabled with one face and the number of revolutions of a motor and the number of faces of the rotary polygonal mirror are eventually decreased. |
