The laser-light refraction method has been performed to investigate the photo-induced cooperative phenomena of an early stage of ferroelasitc and ferroelectric domain formation on KD3 (SeO3) 2 (DKTS) and Rochelle salt (RS) crystals. The refracted light intensity has been observed around the Curie point (Tc). The each temperature dependence of the refracted light intensity under UV irradiation with wavelength of 266nm for DKTS and 400nm for RS with 130fs pulse width shows drastic photoinduced effect in comparison with a non UV irradiation condition. The results clearly demonstrate that the pulsed UV laser irradiation produces a large effect in the embryonic fluctuation near Tc as a photoinduced cooperative phenomenon.
