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Signals derived from a moving shuttle table are utilized to trigger a cavity-dumped YAG laser whose output pulses are directed to machine successive lines of an iron oxide film in a spot-by-spot manner. Machining of the film to form a high-quality reticle requires that the amplitude of the laser output pulses be maintained relatively constant even in the presence of mechanical vibrations and electrical noise which ordinarily tend to produce large fluctuations in the output power of the laser. This is achieved by interposing a phase-locked loop between the output of the shuttle table and the input of the laser. In addition, the loop enhances the machining operation by providing a capability to easily multiply the repetition rate of the pulses derived from the table.