US 7,321,114 B2
Apparatus and method for beam drift compensation
Todd E. Lizotte, Manchester, N.H. (US); and Orest P. Ohar, Hooksett, N.H. (US)
Assigned to Hitachi Via Mechanics, Ltd., Ebina (Japan)
Filed on Mar. 10, 2005, as Appl. No. 11/77,023.
Prior Publication US 2006/0202115 A1, Sep. 14, 2006
Int. Cl. H01J 3/14 (2006.01)
U.S. Cl. 250—234  [250/216; 372/107] 23 Claims
OG exemplary drawing
 
1. An apparatus for maintaining a desired position of a laser beam comprising:
an optical system including first, second, and third prismatic wedges positioned in a path of said beam in spaced-apart relation, the position of said beam being responsive to movement of one or both of said first and second prismatic wedges;
said first prismatic wedge movable along the beam path and having a first, light receiving face and a second face opposite the first face, said first face disposed transverse to the beam path and the first prismatic wedge being tapered in a first direction perpendicular to the beam path;
said second prismatic wedge movable along the beam path and having a first, light receiving face and a second face opposite the first face, said second wedge second face disposed transverse to the beam path path and the second prismatic wedge being tapered in a second direction perpendicular to the beam path and said first direction;
said third prismatic wedge disposed between the first and second wedges and having a first, light receiving face and a second face opposite the first face, wherein the third wedge first face is facing and aligned with the first wedge second face and wherein the third wedge second face is facing and aligned with the second wedge first face;
detector means for detecting an actual position of the beam;
comparison means for comparing the actual position of the beam with the desired position of the beam and generating an error signal representative of the difference between the detected actual position of the beam and the desired position of the beam;
means for moving said first and second prismatic wedges, whereby the optical path of the beam is altered responsive to said moving; and
a position controller responsive to the error signal received from the comparison means and for generating an output signal to said means for moving at least one of said first and second prismatic wedges so that the beam is shifted to the desired beam position.