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Abstract

An optical scanning device (1) includes: a radiation source (4) for supplying a radiation beam (8); a lens system (5) for transforming the radiation beam to a scanning spot (14); and a detection system (6) that includes a quadrant detector (20), an astigmatism generating element (18) for generating a first amount of coma (W.sub.31.sup.a) so as to transform the radiation beam to a first astigmatic radiation beam (21), and a coma correcting element (19) for generating a second amount of coma (W.sub.31.sup.b) so as to compensate the first amount of coma. The coma correcting element includes a correction surface (19A) having a shape defined by a function 'H(r, .theta.)' that includes the term 'A.r.sup.3.cos(.theta.)' wherein: 'H' is the position of the correction surface along the optical axis of the lens system, 'r' and '.theta.' designate polar coordinates, and 'A' designates a first constant dependent on the second amount of coma.

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First Claim