chapter  2
36 Pages

Atomic Motion Preceding a Phase Transition: Birth, Life and Death of Phonons

The advent of femtosecond lasers in the early 1980s has been accompanied

by the development of diagnostic technique for the fast probing of swiftly

excited solid by X-rays, optical and electronic beams with time resolution

of around 10-100 fs. These achievements generated a broad variety of ex-

periments, which allowed observation for the first time new phenomena in

swiftly excited solid on the femtosecond time scale and on the space scale

of tens of nanometers. The most spectacular observations are the oscilla-

tions in the optical probe beam reflection from the laser-excited solid with

the frequency close to that of the cold phonons in the solid [Cheng et al.,

1991; Zeiger et al., 1992]. It was also found that the intensity of X-ray probe

beam diffracted from the laser-excited solid oscillates with the cold phonon

frequency [Sokolowski-Tinten et al., 2003].