Reshaping enhancement of gold nanorods by femtosecond double-pulse laser.

Gold nanorod (Au NR) is an attractive material due to its superior physical and chemical properties. Various applications in diagnostics and biomedicine have been demonstrated. The single-pulse laser is commonly used to reshape nanoparticles in a solvent; however, the laser-material reaction mechanisms underlying nanoparticle reshaping remain unclear. Here, we report the reshaping of Au NRs by ultrafast pump-probe-like double-pulse laser irradiation to understand the reaction dynamics. We demonstrate the enhancement of double-pulse-induced reshaping, which provides an opportunity to design new Au NR structures. It shows that the reshaping enhancement is dependent on the delay time (${\tau _s}$τ) between a pair of separated pulses. The absorption peak wavelength of Au NRs exposed to the shaped double pulse was lower than that of using a single pulse of the same total fluence when ${\tau _s}$τ was less than the electron-phonon relaxation time. This phenomenon was mainly attributed to changes in electronic heat transport and electron-phonon coupling, which affected the pulse delay-dependent nanorod (NR) temperature.