Abstract

In a previous conference, we reported that repeated laser pulses at a single point on an Al thin film can reduce the power needed to melt the surface as compared with cw application.¹ The nature of the damage caused by a single laser pulse of 40 µs at a power too low to cause melting is not easily detected; however, if this same pulse is repeated many times, the surface melts. This multi-pulse effect is a strong function of metal thickness (d) and number of. zaps (N) and is weakly dependent on pulse length. Several mechanisms for this effect were considered, none of which was found to be satisfactory.¹ We propose that this behavior results from cumulative mechanical fatigue due to cyclical thermal stress in excess of the yield stress.

© 1991 Optical Society of America