TELECENTRIC FTHETA LENS SYSTEM OF FOUR-ELEMENT CONSTITUTION

摘要

PURPOSE:To hold the positioning precision of a laser spot high by allowing a lens system consisting of four lenses, i.e. a negative meniscus, a positive meniscus, a positive, and a positive lens to meet specific requirements. CONSTITUTION:The 1st lens has a concave surface on an entrance pupil side, the 2nd lens has a convex surface on an image side, and the 4th lens a plano-convex lens which is arranged close to an image surface at a large distance from the 3rd lens and has a plane surface on the image side. The entrance pupil is arranged at between 0.1f and 0.2f in front of the 1st surface r1 of the 1st lens, and inequalities I -IV hold. In the inequalities, (f) is the focal length of the whole system and ni is the refractive index of the (i)th lens on a line (d); and d6 is the air gap between the 3rd and the 4th lens and f4 is the focal length of the 4th lens. Thus, an f-theta lens system for forming an image of a homogeneous laser beam is obtained.