Laser-induced preferential domain nucleation in hafnium-doped congruent LiNbO 3 crystal

Abstract

The instantaneous preferential domain nucleation effect of the z-cut hafnium-doped congruent LiNbO₃ crystal is investigated. The beam from an Ar-ion laser with 514 nm wavelength is focused on z surface. Two incidence schemes are performed: (1) irradiating near and focusing on the +z surface; (2) irradiating near and focusing on the -z surface. The digital holographic interferometry is used in investigating the visible laser-induced domain nucleation in hafnium-doped congruent LiNbO₃ crystal, and reconstructs the phase shift of new domain. From the investigation of phase shift induced by the domain inversion, the analysis of domain nucleation is performed. When the electric field exceeds a certain threshold value, the preferential domain nucleation is achieved instantaneously at the focal spot during the combined actions of irradiation and external fields. The nucleation fields have a systematic decrease with increasing laser intensity, and reach an effective saturation at higher intensities. The reduction proportions obtained in the second scheme are lower than those in the first one with the same intensity, and the saturation values at higher intensities are the same in both schemes. We attribute the instantaneous effect of laser-induced domain nucleation to the space charge field, and the saturation value at higher intensities is related to the saturation of the space charge field. The formation of instantaneous effect and corresponding physical explanation based on space charge field are present.