Reaching the Shock Limit via Synchronous Laser Excitation of Multiple Ultrafast Acoustic Waves

In recent years, controlling emergent phenomena in correlated materials through collective lattice vibrations has attracted more and more attention. Strain engineering methods favoring superconductivity, ferroelectricity, or adequate for tuning excitonic, magnetic, metal-insulator transitions are among the latest examples. Large elastic static strains of several percents can be applied to bulk or nano samples up to the onset of plasticity or fracture. However, the excitation of ultrashort vibrations carrying out large strains to percent levels—the threshold at which many physico-chemical properties of materials would be significantly perturbed—still remains a challenge. Conventional laser-shock experiments, based on single-shot laser absorption in a transducer layer, can generate the strains required, although at the price of irreversible sample damage and noisy data.

Using ultrafast optics to build up propagative strain waves from the linear to the nonlinear regime, we introduce a non-destructive method of laser-shock wave generation and detection. The methodology is based on the synchronous spatiotemporal laser excitation of numerous distinct photoacoustic sources for additive superposition of multiple strain waves. This technique can efficiently excite substantial strain waves in the range of several percents, up to the mechanical failure, at a kHz repetition rate for optimal detection sensitivity, and offers new possibilities for the extensive study of subtle strain-induced effects in correlated materials where lattice degrees of freedom play a crucial role.