Abstract: An apparatus for detecting the position of a primary beam of electromagnetic radiation, the apparatus including a leaky mirror for reflecting the primary beam and for extracting from the primary beam a secondary beam and a position sensitive detector for detecting the spatial position of the secondary beam, wherein the leaky mirror comprises a material which has a transmissivity of less than 0.2 for the radiation of the primary beam and the position sensitive detector is arranged in the path of the secondary beam after transmission by the leaky mirror, the position of the secondary beam providing a measure of the position of the primary beam.

Abstract: A method for the determination of the surface properties of an object which comprises irradiating the surface of interest with an incident beam of radiation from an optical source, detecting by a detector radiation from the beam scattered by the surface, the detector being located at a predetermined position relative to the surface and the optical source and digitizing and analyzing the image detected by the detector, wherein the incident beam has in cross-section a two dimensional envelope and within the envelope an intensity structure which has multiple edges running in more than one direction which provide information about components of the structure of the beam and the analysis of the image is a two dimensional analysis of the intensity shape and structure of the scattered radiation to provide information about the manner in which the incident beam intensity shape and structure has been changed by scattering at the surface of the object.