A testing apparatus for use with a laser processing system that includes a laser for generating a non-stationary laser beam and a work plane positioned at a working distance relative to the non-stationary laser beam, wherein the testing apparatus includes a support tube; a protective window mounted in the support tube for protecting components mounted within the support tube; a reimaging lens mounted in the support tube for enlarging the non-stationary laser beam for characterization thereof; a pin-hole defining structure mounted in the support tube for receiving laser light generated by the laser beam, wherein the pin-hole is located at a predetermined distance from the reimaging lens; a fiber optic cable disposed within the pin-hole defining structure that has a proximal end at which the laser light is received through the pin-hole and a distal end to which the laser light is delivered; and a photodetector located at the distal end of the fiber optic cable that converts the laser light delivered to the photodetector into electrical voltage output signals based on intensity of the laser light received through the pin-hole.