EDGE DETECTION APPARATUS AND METHOD

An edge detection apparatus for detecting an edge on a surface. The apparatus comprises a source of coherent radiation for generating a radiation beam and directing the beam onto the surface. A radiation detector is located so as to detect radiation diffusely reflected, but not specularly reflected, from the surface. A system is provided for causing relative scanning movement between the radiation beam and the surface. A monitor is coupled to the detector for monitoring the intensity of the detected radiation.