We report on the theoretical and the experimental investigations of the coherent phonon dynamics in sapphire crystal using the femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) technique.The temporal chirped white-light continuum (WLC) is used for the Stokes pulse,therefore we can perform the selective excitation of the phonon modes without using a complicated laser system.The expected quantum beat phenomenon is clearly observed.The theoretical formulas consist very well with the experimental results.The dephasing times of the excited phonon modes,the wavenumber difference,and the phase shift between the simultaneously excited modes are obtained and discussed.This work opens up a way to study directly high-frequency coherent phonon dynamics in bulk crystals on a femtosecond time scale and is especially helpful for understanding the nature of coherent phonons.
We performed femtosecond time-resolved coherent anti-Stokes Raman scattering(fs-CARS) measurements on liquid toluene and PVK film.For both samples,we selectively excited the CH stretching vibrational modes and observed the expected quantum beat signals.The frequency of the well-defined beats is in good agreement with the energy difference between the two simultaneously excited modes,which demonstrates that a coherent coupling between the vibrational modes of the C-H chemical bonds exists at the different positions of the molecules.The dephasing times of the excited modes are obtained simultaneously.
