We have carried out Raman spectroscopic measurements on atactic polystyrene (aPS) under shock compression up to 2 GPa. Observed wavenumber shifts of Raman active modes have been used to determine their Grüneisen parameters and bond anharmonicities. Raman mode at 798 cm−1 displays maximum blue shift of 4.95 cm−1/GPa. Our observed wavenumber shifts under shock compression are found to be consistent with the earlier results obtained under hydrostatic pressure. We have also evaluated pressure through 1D radiation hydrodynamic simulations, and the results are found to be in good agreement with the experimental values. The pressure induced wavenumber shifts and line width changes of the present study can be utilized as a gauge for pressure measurement because of laser induced shock front. Copyright © 2016 John Wiley & Sons, Ltd.
The microscopic and dynamic response of the atactic polystyrene molecules under shock compression at laser power density of 4.9 GW/cm2 was studied using time‐resolved Raman spectroscopy. The shock pressure estimated in the polystyrene sample was 2 GPa, and the temporal and wavenumber resolutions in these experiments were 3 ns and 3 cm−1, respectively. The shocked polystyrene showed a blue shift of 5 and 7 cm−1 for the 1004 cm−1 (C―C―C ring bending mode ν12) and 1606 cm−1 (C―C ring stretching mode νbold8bolda. , respectively. The changes in ν12 and νbold8bolda modes are observed with respect to shock wave propagation. It is observed that the intensities of the Raman peaks decrease and the FWHM of the modes increase due to formation of additional new peaks with delay. The reason behind this indicates the mechanical processes associated with the uniaxial nature of the shock compression. The shock velocity inside the polystyrene was calculated as 2.9±0.12 km/s using the evolution of intensity ratio of peaks with time. This is in good agreement with the shock velocity (3.0 km/s) deduced from the 2D simulations, performed using three temperature radiation hydrodynamic code, THRD. Copyright © 2017 John Wiley & Sons, Ltd.
The damage mechanism induced by laser pulse of different duration in borosilicate glass widely used for making confinement geometry targets which are important for laser driven shock multiplication and elongation of pressure pulse, is studied. We measured the front and rear surface damage threshold of borosilicate glass and their dependency on laser parameters. In this paper, we also study the thermal effects on the damage diameters, generated at the time of plasma formation. These induced damage width, geometries and microstructure changes are measured and analyzed with optical microscope, scanning electron microscope and Raman spectroscopy. The results show that at low energies symmetrical damages are found and these damage width increases nonlinearly with laser intensity. The emitted optical spectrum during the process of breakdown is also investigated and is used for the characterization of emitted plasma such as plasma temperature and free electron density. Optical emission lines from Si I at 500 nm, Si II at 385nm and Si III at 455 nm are taken for the temperature calculations.
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