Polarization Topography in Photorefractive Ferroelectrics

Abstract

Beam-coupling topography is a new holographic technique for spatially resolved studies of induced and spontaneous polarization in photorefractive crystals. I t is especially suited for mapping 180"-domains. In this paper theoretical and experimental fundamentals of the method are outlined. Some results on Bao.29Sro.71Nb206 : Ce are given.

Imaging ferroelectric 180°-domain boundaries by diffraction efficiency topography

“…In the case of SBN only antiparallel domains occur and, hence, we have P, = +P,e,, where e, is a unit vector along the c-axis of the sample. As discussed in [7], the refractive index change An is proportional to the spontaneous polarization P,. Therefore, a transition between antiparallel domains leads to a phase shift of n in the refractive index pattern.…”

“…We use extraordinarily polarized light in order to take advantage of the high electrooptic coefficients of SBN [6]. The diffracted and transmitted beams emerging from the exit face of the sample are imaged onto a CCD chip by two lens systems (see sketch in [7]). In the Fourier plane of the first lens system we can separate both beams.…”

Observation of spontaneous polarization misalignments in periodically poled crystals using second-harmonic generation microscopy

“…But these techniques lack three-dimensional resolution and provide little information of internal structures. More recently, 3D microscopy techniques, such as refractive coupling method [18,19], confocal laser scanning microscopy [20], twophoton luminescence microscopy [21], SHG microscopy/interferometry [22][23][24][25][26], and very recently, optical coherence tomography [27] were adopted to study PPC. Sub-μm resolution of 3D domain structures has been achieved with these scanning microscopies.…”