A laser processing machine head, a laser processing machine head monitoring system, and a method of monitoring an optical element of a laser processing machine feature a light-transmissive optical element and an optical element holder defining a cavity in which the optical element is retained against rotation. A light source mounted to the holder directs a beam of light into the optical element through a peripheral surface of the optical element. A light receiver is responsive to light from the light source reflected through the optical element. Monitoring a signal from the light receiver allows a status of the optical element to be assessed.