Patent ID: 9091633
Filing Date: 2015-07-28
Classification: G01J,G01N

Abstract:
1. A method for locating the centre of a beam profile, comprising the steps of: providing a beam profile; selecting one or more strips through the beam profile; identifying distinct regions of intensity along the one or more strips and labelling them, wherein the step of identifying distinct regions of intensity and labelling them comprises (i) associating one pixel in the beam profile with light reflected at normal incidence from the sample, (ii) associating other pixels in the beam profile each with an angle Θ describing the angle of a light ray which arrives at that pixel, relative to the normal, and (iii) identifying regions of equal angle Θ as labelled regions; calculating an average intensity for each labelled region, using data from the one or more strips; plotting the average intensity against the labelled regions and comparing the results with a plot of the actual intensity obtained by taking a cross-section through the centre of at least one of the one or more strips; and optimising the location of the centre of at least one of the one or more strips by obtaining the best fit between the average intensity plot and the actual intensity plot to thereby identify the centre of the beam profile.