Exploring acoustic strain soliton behavior in materials through numerical simulations and Sagnac interferometry*

Ultrafast laser pulses can be used to generate ultrafast acoustic strain pulses that propagate through materials and are detectable using picosecond ultrasonic techniques. With sufficient pulse energy, and due to the nonlinear elastic propagation within a material, strain textures can have solitary features known as solitons, which travel at supersonic speeds without dispersion, in contrast to lower pulse intensity experiments which propagate conventionally according to linear elasticity.

 

We will discuss numerical simulations of solitons generated from the Korteweg-de Vries equation, using a hypothetical opaque negative thermal expansion (NTE) transducer, as may be realized using films of SmYS or ReO₃. This study reveals that the NTE case yields a soliton train with significantly higher spatial frequencies compared to the conventional positive thermal expansion (PTE) transducers.

 

We will also present progress on the development of an apparatus based on a zero-area Sagnac interferometer that uses an ultrafast laser pulse to generate acoustic strain solitons in materials and detects them after macroscopic propagation. Our approach allows for the generation of multiple strain soliton pulses traveling and interacting within a sample, potentially enabling nanoscale sound-sound interactions to be realized in bulk materials.