Laser‐generated ultrasonic pulses at free metal surfaces

Longitudinal, shear, and surface acoustic pulses have been generated by irradiation of free metal surfaces with a Q‐switched Nd:YAG laser. Laser energies as low as 3 mJ are sufficient to generate ultrasonic pulses, in various metals, that are readily detected by conventional piezoelectric transducers, without the need for laser focusing. The generation efficiency of longitudinal, shear, and Rayleigh modes has been studied in both the presence and absence of a plasma. Experimental data in graphical form highlight several features of the acoustic source, from which a qualitative model is proposed.