F/theta objective lens for focusing scanning laser beam on flat workpiece has concave first lens followed by biconvex aspherical lens followed by optically flat protective glass

摘要

The F/theta objective lens (1) has a tubular housing (5) holding a first lens (2) with a sharply-curved concave upper surface (6) and a sharply-curved convex lower surface (7). A ring-shaped lens support (4) may engage the edge of the convex surface of the first lens. The first lens is followed by a biconvex second lens (3) with a spherical or aspherical upper surface (8) and an aspherical lower surface (9). This is followed by an optically flat protective glass (11) mounted in a holder ring (10).