A novel technique for determining the fusion threshold of metallic sam
ples irradiated by high power laser pulses is presented The technique
uses in situ detection of the acoustic waves produced by the laser pul
se. A pulsed Nd:YAG laser was used, on brass samples, Particular atten
tion has been paid to the measurement of the longitudinal and transver
sal contributions to the acoustic wave. The obtained fluence threshold
for fusion was verified by metallographic analysis and theoretical es
timates.