Femtosecond Laser-Induced Nanowelding: Fundamentals and Applications

Fundamentals of femtosecond laser pulse and nanoparticles are analyzed by a two-temperature model. Ultrafast surface melting, surface nanoengineering and shock wave impact are evident in the surface of graphite by femtosecond irradiation. The interaction between femtosecond laser pulses and Au/Ag nanoparticles has been investigated. Two effects are identified at different intensities: photofragmentation at rather high intensity (~10 W/cm), nanojoining at low intensity (~10W/cm). Photofragmentation forms a large number of tiny nanoparticles with an average size of tens of nanometers. Control over irradiation conditions at intensities near 10 W/cm results in nanojoining of most of the nanoparticles. This nanojoining is obtained in both liquid solution and in solid state thin films assembled from nanoparticles. Nanojoining mechanism is further studied by joining Ag nanoparticles encapsulated by a polymer shell. Nonthermal melting is investigated. Nanojoined Au nanoparticles are expected to have numerous applications, such as probes for surface enhance Raman spectroscopy.