IMPULSIVE STIMULATED LIGHT-SCATTERING STUDY OF ULTRA-SLOW FLUCTUATIONOF FERROELECTRIC TGS

The time domain spectroscopy called impulsive stimulated light scatter ing is developed to investigate the slow dynamics of the structural ph ase transition in the time region from nsec to msec. By the use of thi s new method, the spatially coherent excitations are created in ferroe lectric triglycine sulfate (NH2CH2COOH)(3) . H2SO4 and their time deve lopments are observed. In addition to the acoustic phonon, the mode wi th the characteristic time of tau = 5 similar to 8 mu sec can be first ly observed in this material. The mode intensity shows the lambda type anomaly near the phase transition temperature with remarkable anisotr opy. This mode is identified to be the thermal diffusion mode and is f ound to be the origin of the central peak reported in the light scatte ring experiment.