The New Wave in Shock Waves

Abstract

Laser-driven shock waves (0−5 GPa) can be generated at high repetition rates (100/s) using a moderate-energy tabletop picosecond laser system and a multilayered microfabricated shock target array. High spatial resolution is needed to obtain high temporal resolution of the effects of a steeply rising shock front on molecular materials. The needed spatial resolution is obtained using a sandwich arrangement with a thin layer of sample material termed an “optical nanogauge”. Experiments with an anthracene nanogauge show that ultrafast vibrational spectroscopy can be used to determine the shock temperature, pressure, velocity, and shock front rise time. Shock pulses can be generated with rise times <25 ps, which generate irreversible shock compression, and with rise times of a few hundred picoseconds, which generate reversible compression. These pulses, which have a duration of a few nanoseconds, are termed “nanoshock” pulses. Nanoshock pulses produce large-amplitude mechanical perturbations and can initiate and turn off thermochemical reactions, produce highly excited vibrational populations, and heat and cool condensed matter systems at tremendous rates. These applications are illustrated briefly in nanoshock experiments on an energetic material and a heme protein. Using high repetition rate nanoshocks to study large-amplitude molecular dynamics in molecular materials important in chemistry and biology is the new wave in shock waves.

Orientation Dependence in Molecular Dynamics Simulations of Shocked Single Crystals

“…Shock wave physics is becoming yet another fertile area for atomistic studies. Laser-driven shock waves through samples tens or hundreds of nanometers thick can be probed by spectroscopy [3] or interferometry [4] with picosecond time resolution, time and length scales well within the capabilities of modern MD simulations [5].Previous studies of shock waves in 3D solids have primarily considered fcc Lennard-Jonesium with shocks traveling in the ͗100͘ direction [5][6][7]. An important first step to extending these simulations toward more realistic materials, which may include preexisting defects, dislocations, and grain boundaries, is the study of orientation-dependent effects on shock propagation in single crystals.…”

In situRaman spectroscopy of shock-compressed benzene and its derivatives

“…Some sophisticated applications of laser spectroscopy to in situ observation of shock-induced phenomena have been reported over the last couple of decades. [1][2][3][4][5][6] In this paper we report shock-induced changes in vibrational spectra of benzene, iodobenzene, and nitrobenzene measured by a single-pulse laser Raman spectrometer in conjunction with a plate impact technique. It was found that shock-induced changes in Raman spectra of nitrobenzene are quite different from those of benzene and iodobenzene.…”

Ultrafast Dynamics of Shock Waves in Polymers and Proteins: The Energy Landscape

“…The probe pulses interrogate a region of ϳ20 mm in diameter at the center of the ϳ100 mm diameter nanoshock [9]. In this central region, the pressure and velocity at the nanoshock front remain constant for several nanoseconds [1,9,10], showing we are observing compression by an approximately planar shock front.…”

“…The BSA film is a crude model for a dry biological tissue such as skin. The nanoshock technique and the laser apparatus have been discussed previously [1,9,10]. A schematic of the experiment is shown in Fig.…”

“…To probe such a thin layer, a sensitive technique has been developed using resonance coherent anti-Stokes Raman spectroscopy (CARS) of a dye in the sample. After shock layer ablation ϳ1.2 ns after the near-IR pulse, broadband multiplex CARS spectra are obtained [10]. One pulse at ϳ595 nm has a narrow spectral bandwidth ͑ϳ1.5 cm 21 ͒ which determines the spectral resolution.…”