ACHROMATIC SCANNER HAVING A MONOCHROMATIC F-THETA OBJECTIVE

摘要

An achromatic scanner in which pre-scan optics and post-scan optics are designed and disposed with respect to one another in such a way that for a light beam imaged onto the target surface a first image plane of the pre-scan optics coincides with a first object plane of the post-scan optics for a first beam portion and a second image plane of the pre-scan optics coincides with a second object plane of the post-scan optics for a second beam portion, wherein an image plane of the post-scan optics which lies on the target surface is associated with the first object plane of the post-scan optics and the second object plane of the post-scan optics.

主权项

1. Achromatic scanning device comprising a light source a scanning unit formed with a rotatable polygon mirror, having a polygon angle; a pre-scanning optical system upstream of the polygon mirror, for shaping and guiding a light beam which is emitted from the light source onto the polygon mirror, wherein the light beam has a first beam component having a first wavelength and a second beam component having a second wavelength as well as a post-scanning optical system, said post scanning optical system being downstream of the polygon mirror and being formed by an f-theta lens for shaping and guiding the light beam deflected by the polygon mirror into a scan direction onto a target surface which is arranged in an image plane of the post-scanning optical system for the two beam components, wherein
the post-scanning optical system is monochromatic, so that an imaging in an ideal image position occurs only for a light beam with one wavelength, said pre-scanning optical system and said post-scanning optical system being designed and arranged with respect to each other in such a way that for a light beam, which is imaged onto the target surface, a first image plane of the pre-scanning optical system in a first image-sided intersection length coincides with a first object plane of the post-scanning optical system for the first beam component; and a second image plane of the pre-scanning optical system in a second image-sided intersection length coincides with a second object plane of the post-scanning optical system for the second beam component, wherein the first object plane of the post-scanning optical system and the second object plane of the post-scanning optical system are assigned the image plane of the post-scanning optical system, so that the longitudinal chromatic aberration is corrected for the two beam components, and wherein for the first beam component the post-scanning optical system has a first image-sided focal length, and a second image-sided focal length for the second beam component, where both image-sided focal lengths satisfy the following equation:
2f′postλ1Wp+fpostλ1Ws1(Wp; s′preλ1)=2f′postλ2Wp+f′postλ2Ws2(Wp; s′preλ2), where Ws1 is an angle component of the first beam component; and Ws2 is an angle component of the second beam component, and tan (Ws) ≈Sw/2* sin (Wp)/s′preλ1 and tan (Ws2) ≈Sw/2* sin (Wp)/s′preλ2, where Sw is the key width of the polygon mirror, with which the transverse chromatic aberration is also corrected for the two beam components.