Abstract: A method of compensating for sample misalignment in an optical measurement apparatus (40), comprises the steps of: determining an expected response from a detector (58) in said optical measurement apparatus given a particular set of parameters defining a path that light can take through the optical measurement apparatus from a source (42), via a sample (50), to the detector (58); measuring a response from the detector for the sample under test; and refining the set of parameters until the expected response and the measured response converge so as to determine the set of parameters giving rise to the measured response.

Abstract: A method for locating the centre of a beam profile, comprises 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 consistently; calculating a combined 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 so as to obtain the best fit between the average intensity plot and the actual intensity plot to thereby identify the centre of the beam profile.