LASER-BEAM DEFLECTION MONITORING OF ND-YAG LASER ABLATION - PULSE SHAPE AND REPETITION RATE EFFECTS

The laser beam deflection probe has been employed to study blast waves generated during ablation of metallic surfaces by sequences of 1.06 mum Nd : YAG laser pulses separated by less than 1 mus. A fluence threshold has been found, below which the effects of individual pulses can be resolved by the laser probe. Above that, the deflection signal has a similar form as if the surface were irradiated with a single pulse. Analysis of the signals in terms of the spherical blast wave theory shows that a pulse sequence generates a weaker blast wave than a single pulse of equal total energy. On the other hand, the sequence yields a higher etch depth than the single pulse.