Stimulated Raman scattering of lattice translational modes in liquid heavy water

Abstract

A study was conducted on stimulated Raman scattering (SRS) when laser-induced plasma is formed in heavy water by focusing an intense picosecond pulsed Nd:YAG laser beam with wavelength 532 nm at room temperature. An unexpected 280 cm(-1) low frequency SRS line attributed to the lattice translational modes is observed. This SRS line and the internal-mode SRS lines indicate that the ice VII structure is formed in heavy water under the condition of laser-induced shockwave production.

Onset of ice VII phase during ps laser pulse propagation through liquid water

“…Ice VII is a cubic crystal consisting with no connecting hydrogen bonds passing through the center of water hexamers between two interpenetrating cubic ice lattices 11 . A similar observation was reported earlier using high energy ns laser pulses confirming the formation of ice VII structure at different pressures 1,4,7,12 . With the increase in input energy, GPa range pressures are formed at focal volume increasing the OH bond length.…”

“…However, most of the work is concentrated on the different structural formations like ice VII, ice VIII and ice X [1][2][3][4] . Of the various structures, ice VII has been explored frequently using A 1g vibrational stretching mode in water (H 2 O) and using translational modes in heavy water (D 2 O) 1,4,5 . Ice VII or VIII has A 1g , E g and B 1g internal modes corresponding to in-phase, antisymmetric and out-of-phase stretching modes 1,6 respectively which occur at shifts less than 3400 cm -1 .…”

“…All the above measurements have been concentrated more on the internal mode stimulated Raman scattering (SRS) shifts corresponding to different pressures to confirm ice VII formation. Ice VIII and ice X mostly have been explored based on the translational mode shifts corresponding to different pressures 5,7,8 . We present the internal mode SRS and translational shifts confirming the formation of ice VII at pressures in the range of GPa pressures during propagation of 30 ps pulses through liquid water.…”

Estimating the pressure of laser-induced plasma shockwave by stimulated Raman shift of lattice translational modes

“…Laser shockwave compression can cause structural change in a liquid substance and new substance formation. [6][7][8] The pressure of the shockwave is important to understand new substance formation. The peak-pressure of the shockwave during plasma formation on picosecond or nanosecond time scale has been measured using hydrophone and time-resolved photography.…”

“…16,17 Laser-induced breakdown mechanism in water and heavy water, as well as in other liquids, has been well studied. 7,[18][19][20] The breakdown starts after absorption of the focused laser light by persistent molecules. The absorbed energy forms high-pressure vapors, which support avalanche ionization in that area.…”