ULTRAHIGH TIME-RESOLUTION VIBRATIONAL SPECTROSCOPY OF SHOCKED MOLECULAR-SOLIDS

A method is described for obtaining ultrahigh time-resolution vibratio nal spectra of shocked polycrystalline materials. A microfabricated sh ock target array assembly is used, consisting of a polymer shock gener ation layer, a polymer buffer layer, and a thin sample layer. A near-I R pump pulse launches the shock. A pair of delayed visible probe pulse s generate a coherent anti-Stokes Raman (CARS) spectrum of the sample. High-resolution Raman spectra of shocked crystalline anthracene are o btained. From the Raman shock shift, the shock pressure is determined to be 2.6 Gpa. The rise time of shock loading is 400 ps. This rise tim e is Limited by hydrodynamics of the shock generation layer. The shock velocity in the buffer layer is found to be 3.7 (+/-0.5) km/s, consis tent with the observed shock pressure. As the shock propagates through a few mu m of buffer material, the rise time and pressure can be moni tored. The rise time decreases from similar to 800 to similar to 400 p s over the first 6 mu m of travel, and the pressure begins to decline after about 12 mu m of travel. The high-resolution CARS method permits detailed analysis of the vibrational line shape. Simulations of the C ARS spectra show that when the shock front is in the crystal layer the spectral linewidths are inhomogeneously broadened by the distribution of pressures in the layers. When the crystal layer is behind the fron t, the spectral linewidth can be used to estimate the temperature. The increase of the spectral width from the ambient 4 to similar to 6.5 c m(-1) is consistent with the expected temperature increase of similar to 200 degrees. (C) 1997 American Institute of Physics.