Ultrafast lasers for nanomaterial growth and processing

Summary form only given. As robust sources for an increasing number of industrial applications, ultrafast lasers with sub-picosecond pulse duration have experienced a steady growth over the past decades. In this presentation, recent progress of ultrafast laser-based nanoscale material growth and processing will be discussed, along with selected emerging applications of laser-produced nanomaterials in the development of renewable energy technologies. One example of energy technologies that has benefited greatly from laser-based materials development is efficient electricity transmission by utilizing high critical temperature superconductor wires. Pulsed laser deposition, which typically involves applying a nanosecond laser beam to ablate a target material followed by depositing the precursor vapor onto a substrate, is an effective technique for developing superconductors as well as many other industrial materials. However, a main technical obstacle for making materials at the nanometer scale using nanosecond lasers is the formation of micron-sized particulates from the ejected melts. Ultrafast lasers, with pulse duration shorter than the characteristic time of thermal diffusion, enable nanomaterials fabrication with reduced micro-sized particulates when operated in the so-called non-thermal ablation regime. Under very high irradiation power of ultrafast lasers, electrons in the target material can be heated much faster than they are cooled through electron-phonon interactions. Emission of high-density energetic electrons from the target surface can take place, followed by separation between the escaped electrons and the positively charged parent ions, which eventually leave the surface with the buildup of a strong electric field. Consequently, ultrafast laser pulses are able to ablate solid materials without encountering significant thermal processes (e.g., melting), therefore enabling high quality nanomaterial growth. In the meantime, direct write of nanoscale struc- tures with minimal lateral damage in the material can be realized. Utilizing femtosecond laser pulses, we are developing a variety of nanomaterials and nanostructures that have practical applications for high capacity solid-state hydrogen storage and high efficiency solid-state lighting.