Structural studies of melting on the picosecond time scale

Abstract

Ultrafast structural studies of laser-induced melting have demonstrated that the solid-liquid phase transition can take place on a picosecond time scale in a variety of materials. Experimental studies using ångström wavelength X-rays from the sub-picosecond pulse source at Stanford (now retired) on non-thermal melting of semi-conductors, such as indium antimonide, employed the decay of a single Bragg-peak to measure the time component of the phase transition. These materials were found to start melting within one picosecond after the laser pulse. Recent computer simulations have described the thermal melting of ice induced by an infrared laser pulse. Here it was shown that melting can happen within a few picoseconds, somewhat slower than non-thermal melting in semi-conductors. These computer simulations are compatible with spectroscopy experiments on ice-melting, demonstrating that simulations form a very powerful complement to experiments targeting the process of phase-transitions. Here we present an overview of recent experimental and theoretical studies of melting, as well as new simulations of ice-melting where the effect of the size of the crystal on scattering is studied. Based on simulations of a near-macroscopic crystal, we predict the decay of the most intense Bragg peaks of ice following heating by laser pulse, by modeling the scattering from the melting sample in the simulations.

Picosecond dissociation of amyloid fibrils with infrared laser: A nonequilibrium simulation study

“…was applied to mimic a laser pulse. 26,27 Here, E 0 represents the amplitude of the electric field, σ is the pulse width, t is the time after the pulse maximum t 0 , c is the speed of light, and ω is the frequency. This technique has been implemented in the GROMACS simulation package.…”

Molecular dynamics study of congruent melting of the equimolar ionic liquid-benzene inclusion crystal [emim][NTf2]•C6H6

“…Cold-stage polarizing microscopy, NMR, and combination of laser pumping with x-ray scattering probing have also been used for this purpose. 1, 32 Parallel to experiments, computational modeling can greatly aid in understanding the melting process and producing a quantitative link between the melting point and chemical structure of ionic materials. Many molecular dynamics ͑MD͒ simulation studies of ILs with accurate force fields have been performed since 2001 ͑see Ref.…”