Towards a new generation of acoustic imaging

Although laser ultrasound imaging is now recognized as a powerful tool for investigating elastic properties in a wide range of fields, from applications to fundamental research, a number of obstacles remain. The generation of acoustic fronts by femtosecond lasers, with wavelengths of a few tens of nanometers, ensures excellent depth resolution, but has so far failed to achieve such resolution in the layer plane.

To solve this problem, researchers from INSP’s Acoustics for Nanosciences team have proposed coupling optical pump-probe approaches with near field microscopy concepts, paving the way for 3D acoustic imaging on the scale of a few nanometers.

a) Schematic diagram of excitation. A finite element simulation is used to describe for the guidance of a longitudinal L and transverse T wave. 

b) Impedance mapping on a gold silicon substrate. The lateral resolution estimated here is of the order of 250nm, i.e. a factor of 10 lower than the resolution achievable with conventional acoustic imaging.