Patent ID: 7362424
Filing Date: 2008-04-22
Classification: G01N

Abstract:
1. An apparatus for determining the position of a radiation beam, comprising: (a) a first reflective surface and a second reflective surface, said reflective surfaces being placed to form the reflective exterior of a wedge; (b) a first detector placed to detect radiation reflected from said first reflective surface, (c) a second detector placed to detect radiation reflected from said second reflective surface, wherein said first and second detectors are placed to selectively detect radiation reflected from different surfaces of said wedge; (d) a differential amplifier, wherein said differential amplifier compares the intensity of radiation detected at said first and second detectors; (e) a third reflective surface placed to reflect radiation to said first and second reflective surfaces; (f) a positioning device attached to said third reflective surface; and (g) a feed back circuit, wherein a signal from said differential amplifier directs said positioning device to change the position of said third reflective surface.