Softening Mechanism of Coherent Phonons in Antimony Under High Density Photoexcitation

Abstract

We have investigated the dynamical properties of coherent phonons generated in antimony under high density photo excitation. Precise measurements and extended analysis of coherent phonon oscillations provide new insights into the process of impulsive softening. In the process of recovering from instantaneous softening, phonon frequency shows an unexpected temporal evolution involving an abrupt change and a slight overshoot. Moreover, fluence dependence of the initial phonon frequency is strongly correlated with the phonon frequency shift of the high-pressure Raman spectra.These results clearly prove that the structural changes (lattice contraction and expansion) induced by laser excitation governs the softening mechanism of coherent phonons.

Novel Theory for Transient Light Matter Interaction

“…Time-resolved diffraction experiments with x-rays and electrons [15][16][17] under high-density excitation reveal surprisingly large lattice displacements; however, insufficient temporal and spatial resolution obscures the effect. Conversely, the strain modulation of coherent phonons in antimony [18] could provide additional information about the effect. The reduction of the frequency of the coherent phonon immediately after the high-density pulse excitation can be explained by the lattice strain.…”