Non-contact ultrasonic generation and detection by lasers

In optically opaque solids broadband ultrasonic pulses can be generated by short laser pulses via the thermoelastic effect at small laser intensities (smaller than 10 MW/square centimeter). At large optical intensities (bigger than 10 MW/square centimeters) ablation of surface material sets in causing recoil which results in strong and broadband pressure pulses. In conjunction with optical interferometry, both mechanisms allow one to carry out noncontact inspection of materials and components by ultrasound. Applications of this technique are discussed together with a critical assessment of possible future developments.