A Position Sensitive Detector (PSD) consists of a monolithic PIN photodiode with a uniform resistance in one or two dimensions.  PSDs have many advantages, compared to discrete element detectors, including high position resolution, fast response speed and simple operating circuits. Position data is independent of the size of light spot on the detector. They can be used for non-contact distance measurement, laser beam alignment and optical tracking of an object. PSDs for tracking electrons or high energy particles are also available.