LASER GENERATION OF ULTRASONIC LAMB WAVES USING LOW-POWER OPTICAL SOURCES

Laser generated ultrasound is convenient noncontact broad bandwidth so urce of test radiation for ultrasonic nondestructive evaluation (NDE). However, conventional laser ultrasound exploits high pulse energies i n short duration pulses typically involving peak powers in the tens to hundreds of megawatts range. Consequently, surface damage is frequent ly problematic. The prospects are examined for low peak power sources based on laser diode excitation of mechanical samples. With peak power s of significantly less than 1W and a 2% duty cycle, the authors have demonstrated broadband Lamb wave excitation in a thin metal sample, in cluding observation of the dispersion curves. The same principle can b e extended to full continuous wave (CW) operation. This enhances the r eceived SNR while involving minimal probabilities of sample damage.