Coherent Raman spectroscopy of nanoshocks

Abstract

A new technique is described, where picosecond laser pulses generate and probe 4.2 GPa nanoshocks in polymeric and polycrystalline solids at a high repetition rate of ∼100/s. The term nanoshock refers to the short duration (a few ns) of the shock pulse and the very small shocked volume (a few ng). The nanoshock wave form is characterized by the shock front risetime, shock falltime, peak pressure, and velocity. Coherent Raman spectroscopy during nanoshock propagation in a 700-nm-thick layer of polycrystalline anthracene, called an optical nanogauge, is used to determine these quantities. A powerful method of analysis, singular value decomposition (SVD), is applied to Raman spectroscopy of shock waves for the first time. Using SVD analysis, the risetime of the nanoshock pulses is found to be less than 25 ps, and the velocity of the shock front in the nanogauge is monitored in real time. Some possible applications of nanoshock technology in the areas of shock-induced material transformation and shock-induced mechanical deformation processes, are discussed briefly.