Opto-Acoustics and Laser Ultrasonics

The aim of opto-acoustics research is to introduce innovative methods for generating and detecting acoustic waves using lasers, for acoustic assessment and non-destructive testing of materials and structures.

Here, the role played by the piezoelectric transducer in traditional ultrasonic measurements is assigned to a laser, but the latter can play this role remotely and without any contact with the materials. If required, sound excitation and detection can be very local (down to the micron scale, the diameter of the focused laser beam) or, on the contrary, can rapidly and optically scan large surfaces (up to a few meters).

In addition to other frequency ranges accessible by traditional methods, opto-acoustics gives access to hypersonic frequencies of acoustic waves (above 1 GHz). In particular, acoustic waves with frequencies above 10 GHz have wavelengths shorter than the micrometer in solids. This makes laser-generated and detected hypersonics a unique tool for the non-destructive evaluation of nanocrystalline materials and nanostructures, as well as for three-dimensional imaging inside continuously inhomogeneous media with nanometer-scale axial resolution.

The contactless principle of this technique makes it particularly suitable for evaluating materials in hostile environments, such as very high temperatures and/or very high pressures, making it a very interesting control tool for both fundamental research and industrial applications.