Method and apparatus for reducing or eliminating stray light in an optical test head

摘要

An optical test head comprises one or more optical input paths by which a beam of light is communicated from a light source to a workpiece and one or more optical output paths by which light reflected off of the workpiece is communicated to a detector. The input optical path and the output optical path can include one or more mirrors and one or more lenses. At least one of the optical paths includes a layer for trapping and/or absorbing stray light. One or more of the lenses includes an anti-reflective coating for reducing noise caused by unwanted light reflection off of the lenses. The optical paths include one or more masks reducing stray light. The one or more masks can have an adjustable aperture (e.g. an iris).