Rayleigh wave and super-shear evanescent wave excited by laser-induced shock at a soft solid–liquid interface observed by photoelasticity imaging technique

We investigated laser-induced shock excitation of elastic surface waves at a free surface and a soft solid–liquid interface using a custom-designed photoelasticity imaging technique. Epoxy-resin and pure water were selected as the solid and liquid media. The elastic surface waves were excited via a shock process induced by focusing a single nanosecond laser pulse on the solid surface. To confirm the experimental observations, the roots of the Rayleigh and Stoneley equations were calculated. For a free surface, we present an entire-field observation of elastic surface waves, which includes a super-shear evanescent wave (SEW) that propagates faster than the shear wave but slower than the longitudinal wave. For a soft solid–liquid interface, we demonstrate the presence of a non-leaky Rayleigh wave that corresponds to a real root of the Stoneley equation. We also evidence the existence of a SEW that propagates 1.7 times faster than the shear speed in the solid and corresponds to a complex conjugate root of the Stoneley equation. These results correct the previously accepted notion that the Scholte wave is the only surface wave that can be generated at a soft solid–liquid interface.