Patent ID: 7697726

Claim:
Apparatus for determining a surface characteristic of a composite material sample surface, the apparatus comprising an interferometer system having: a light director to direct light along a sample path towards a sample surface and along a reference path towards a reference surface such that light reflected by the sample surface and light reflected by the reference surface interfere; a mover operable to effect relative movement along a measurement scan path between the sample and the reference surface; a sensing device having an array of sensing elements each operable to sense light representing the interference fringes produced by a corresponding surface region of the sample surface; and a controller operable to carry out a measurement operation by causing the mover to effect relative movement while the sensing device senses light intensity at intervals to provide, for each surface region, a set of intensity data representing interference fringes produced by that surface region; and the apparatus also comprising a data processor providing: a position determiner to determine from the set of intensity data obtained for a surface region of the sample surface surface height data representing a position on the measurement scan path that corresponds to the height of that surface region of the sample surface; an amplitude determiner to determine for a surface region of the sample surface amplitude data representing the amplitude of the set of intensity data obtained for that sample region of the sample surface at the position determined by the position determiner to represent the height of the surface region; a correction parameter provider to provide a correction parameter; and a modified surface height calculator to calculate modified surface height data for a surface region of the sample surface by modifying the surface height data determined by the position determiner for that surface region by a correction factor determined using the corresponding amplitude data determined for that surface region and the correction parameter provided by the correction parameter provider.