Abstract: An apparatus for detecting the presence of a workpiece on a polishing pad of a chemical mechanical polishing (CMP) machine employs an optical interrogation signal that is applied during the CMP process. An optical probe assembly produces a light signal that communicates with the polishing pad; portions of the light signal reflect from the polishing pad in a scattered manner. A light receptor receives reflected light associated with the interrogation signal, and the characteristics of the received light are analyzed and processed by a processor used by the apparatus. By analyzing the scattered light signals, the apparatus distinguishes the reflective characteristics of the polishing pad from the reflective characteristics of the workpiece. Thus, the apparatus is capable of detecting a lost or broken workpiece in a fast and effective manner.