Picosecond Dynamics Behind the Shock Front

Abstract
Understanding the microscopic details of shock-wave initiation of energetic materials requires a realistic picture of picosecond time scale processes occurring in large molecules located in an ≈100 nanometer thin layer just behind the front. In this paper, I discuss a theoretical model for shock wave induced chemistry which highlights the role of molecular mechanical energy transfer processes, especially multiphonon up-pumping. Picosecond laser measurements of multiphonon up-pumping in a high explosive, nitromethane, are presented. Up-pumping occurs on the ≈100 picosecond time scale in nitromethane. The fundamental problem in direct measurement of the states of molecules just behind a shock front is simultaneously achieving picosecond time resolution and nanometer space resolution. A new method for probing dynamics immediately behind a shock front using optical nanogauges is described, and some preliminary results are presented.