Influence of pulse width and detuning on coherent phonon generation

Abstract

We investigated the coherent phonon generation mechanism by irradiation of an ultrashort pulse with a simple two-level model. Our derived formulation shows that both impulsive stimulated Raman scattering (ISRS) and impulsive absorption (IA) simultaneously occur and phonon wave packets are generated in the electronic ground and excited states by ISRS and IA, respectively. We identify the dominant process from the amplitude of the phonon oscillation. For short pulse widths, the ISRS is very small and becomes larger as the pulse width increases. We also show that the initial phase is dependent on the pulse width and the detuning.

Dynamic Jahn-Teller viewpoint for generation mechanism of asymmetric modes of coherent phonons

“…We then discuss the dependence of the phonon amplitude on the polarization of the pump-pulse. We find that, as observed previously [13], the IA and the ISRS paths coexist as distinct quantum processes, and both display the same dependence of the amplitude of the coherent phonons on the polarization angle. The IA mechanism predominates over the ISRS process with respect to the generation efficiency in the opaque region except for the case of excitation to the band-edge, where the IA and ISRS processes compete in terms of the generation efficiency.…”

“…Then, in the limit of zero band-width, Q 1 (t) reduce to those obtained in Eqs. (19) and (22), respectively, in our previous work [13].…”

“…Excitation in the opaque region is more problematic to explain, because the resonant ISRS and DECP paths should coexist according to quantum mechanics. Recently, we conducted a theoretical study using a simple two-level model to clarify the relationship between the ISRS and DECP mechanisms by applying a density matrix formalism [13]. We showed that the ISRS and DECP paths coexist as distinct quantum processes, especially in the case of resonant excitation.…”

Coherent control theory and experiment of optical phonons in diamond

“…Let us consider a two-level system for the electronic state coupled with a harmonic oscillator. 36,51 The Hamiltonian is given by…”

“…33,34 To understand the unified generation mechanism of coherent phonons, the microscopic theory based on quantum dynamics is required. [35][36][37][38] However, in the coherent control experiment, the amplitude and phase dependences have been not yet understood from these microscopic theories.…”