Abstract
Dynamics of coherent phonons in a ferroelectric film of PbTiO3 is investigated using femtosecond time-resolved transient reflection measurements with a pump and probe technique. Coherent optical phonons are generated by irradiation of a femtosecond laser pulse via impulsive stimulated Raman scattering. Four coherent oscillations with frequencies of 3.2, 4.7, 6.2 and 8.6 THz are observed and assigned to optical phonons of A1(1TO), A1(1LO), E(2TO), and \({\mathrm{B}}_{1} + \mathrm{E}\) modes, respectively. A positive frequency chirp is observed in the soft mode (A1(1TO)) within 2 ps, and explained by relaxation of vibrational states and anharmonicity of the potential curve in the soft mode coordinate.
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