Coherent Excitation of Ferroelectric Soft B₂ Mode of KDP by Impulsive Stimulated Raman Scattering

Abstract

Coherent excitation of the ferroelectric soft modes of KDP has been done in the time domain by femtosecond impulsive stimulated Raman scattering. The observed time dependence shows clearly a relaxational character of the soft mode in a wide temperature range above T_c. A critical slowing-down is directly revealed in the temperature dependence of the relaxation time τ = τ₀ T₀/(T-T₀) as τ₀ is 0.11 × 10^-12 s, where T₀ is the phase transition point of the clamped crystal. The order-disorder phase transition mechanism is reasonable within the limit of the time resolution of the present study.