A sensing apparatus monitors a cover optic on a laser processing head for contamination, indicating the need to replace the cover optic. The apparatus includes at least one reflector and at least one sensors that are disposed in the processing head adjacent a periphery of the cover optic. The reflector reflects radiation from the laser beam deflected from contamination on the cover optic and incident thereagainst. The sensor is offset from the reflector and detects at least a portion of the radiation reflected by the reflector. A controller in communication with the sensor can determine the contamination on the cover optic based on the detected radiation.