Single-pulse diffraction imaging of ultrafast melting in gold nanorod

Ultrafast light–matter interaction invigorates research activities on light induced quantum control of materials properties by providing routes to explore new phases of matters in nonequilibrium states. With the exclusive excitations of electrons through femtosecond IR laser pulses, various physical processes can be accessed mode selectively, which enables the way to tackle fundamental science issues including the role of electrons in driving crystal phase changes. Au nanorod, are elongated gold single nanoparticle that has longitudinal localized surface plasmon resonance (LSPR). Understanding this surface plasmons in Au nanorod is essential, which enables to control optical properties in metal nanostructures. Despite the significance of surface plasmons in the light-matter interaction in metallic nanoparticles, the role of the localized surface plasmon resonance in ultrafast melting has remained elusive. We studied the impact of surface plasmons dynamics in ultrafast phase transition of Au nanoparticle using femtosecond pump-probe X-ray imaging at PAL-XFEL. To study further, we directly imaged the reaction dynamics of photoinduced Au nanorod with femtosecond X-ray pulses. Shape distortion caused by LSPR and further investigation of laser fluence and polarization direction dependence was carried out to result in various melting reaction in reaction in response to the surface plasmon excitations in metallic nanoparticles.