PREMELTING AND MELTING EFFECTS ON WAVE-FORM OF LASER GENERATION ULTRASOUND

The epicenter waveform for the metals with the different thermal diffu sivities are excited by pulsed laser and detected by laser interferome ter. The experimental results show that the epicenter waveform depends strongly on the power density of laser when a single shot of laser is used. It also depends strongly on the times of shots of laser when th e power density (or fluence) of laser is fixed. The relations between the epicenter waveform and the power density of laser as well as the s hots of laser show that the melting depth is a physical reason for app earance of precursor.