Ultrafast spectroscopy of laser-initiated nanoenergetic materials

A picosecond laser flash-heating technique is combined with ultrafast spectroscopic probe diagnostics to investigate the fundamental mechanisms of nanoenergetic material performance. The systems studied include Al nanoparticle aggregates in nitrocellulose (NC) oxidizer, size-selected Al nanoparticles in NC and in Teflon oxidizers, and nanoparticle thermites consisting of 30 nm Al and nanometric MoO₃. The time-dependence of reactions between Al and the oxidizer on the picosecond to nanosecond time scales are studied using coherent anti-Stokes Raman scattering (CARS) to monitor oxidizer consumption. The time-dependence of energy release is measured using fast optical spectroscopy. The space-dependence of chemical reaction propagation over 100 to 1500 nm distances is studied using the average distance between nanoparticles as a ruler. The distance of reaction propagation from a flash-heated Al nanoparticle increases linearly with energy, which is explained by a hydrodynamic model.