DIRECT OBSERVATION OF THE FERROELECTRIC SOFT MODE OF KDP BY IMPULSIVESTIMULATED RAMAN-SCATTERING

Impulsive stimulated Raman scattering experiments are performed in KDP to observe the ferroelectric soft mode directly in time domain. The o bserved ferroelectric B-2 mode shows a complete single exponential tim e decay after the electronic excitation spike around the time origin. The temperature dependence of the ralaxational time tau follows tau = tau(0)T(0)/(T-T-0), here T-0 is the phase transition temperature of th e clamped crystal and tau(0) is obtained to be 0.11 x 10(-12) s which shows a good agreement with previous studies.