Abstract
A method of calibrating an apparatus configured to perform optical coherence tomography to measure depth of an article of a prescribed type comprises (a) using an existing measurement system configured to measure depth, measuring a sample of the article to obtain reference depth measurements; b) using the optical coherence tomography apparatus, capturing sectional images of the sample at the same positions at which the reference depth measurements were obtained; c) determining, in each sectional image, a number of pixels in a depth direction of the sample; and d) determining, using the reference depth measurements and the numbers of pixels from the sectional images, a correlation curve to associate pixels in images captured by optical coherence tomography with physical depth. Measuring the sample comprises performing plural measurements at different positions on the sample. Each measurement is in the form of a profile of the sample at a corresponding position thereon.