| 摘要 |
PURPOSE:To vary the size of a spot continuously by providing a zoom lens optical system in front of a laser beam image formation optical system consisting of plural cylindrical lenses. CONSTITUTION:A convex lens 10, a concave lens 11, and a convex lens 12 form an afocal lens optical system, and cylindrical lenses 13 and 14 form an optical system for obtaining an elliptic focus. When an incident laser beam L has a Gaussian intensity distribution symmetrically about the center, the ratio of the minor and major axes of the elliptic shape of the laser beam spot is determined by the cylindrical lenses 13 and 14, so the spot size (d) can be varied by varying the diameter D of the beam incident on the cylindrical lens system by the zoom function of the concave lens 11 which becomes a variator and the convex lens 10 which becomes a compensator associatively. Namely, while the ratio of the minor axis and major axis of the elliptic shape of the laser beam spot is held constant, the size of the laser beam spot can be varied continuously.
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