Ultrafast Spectroscopy of Energetic Materials and Energetic Mechanical Processes.

摘要

The goal of this project is to develop a fundamental understanding of fast mechanical processes at a molecular level. It is believed that this fundamental research will lead to a clearer understanding of energetic mechanical processes relevant to the AFOSR mission and in the broader world as well. These include the following: (1) impact initiation of energetic materials; (2) mechanical failure by debonding, cracking, or spallation; (3) lubrication dynamics of high speed parts; and (4) fast combustion of metal particle/oxidizer composites. These processes are induced by laser-generated shock waves, laser heating, or specific vibrational pumping with tunable femtosecond mid-infrared pulses. These perturbations are followed by fast infrared or Raman probing to study the vibrational transitions of mechanically perturbed molecules or materials. Mid-infrared absorption creates a highly nonequilibrium vibrational population whose relaxation is relevant to all highly energetic chemical processes. Shock waves create high pressure, large amplitude structural perturbations, high temperatures, and large strain rates. Using ultrafast shock compression, the authors could initiate energetic chemistry, cracking, debonding and spallation, and produce stress on liquids at solid interfaces that mimics the stress felt in high speed engines. Laser flash heating is used to heat metal nanoparticles embedded in oxidizing matrices. The hot metal particles can then undergo fast energetic oxidization chemistries.