All-optical three-dimensional mapping of 180° domains hidden in a BaTiO_3crystal

Abstract

We present three-dimensional, high-contrast maps of 180 degrees domains hidden inside photorefractive crystals of BaTiO(3). Some domains are columns that run the entire length of the crystal, whereas others are short needles that begin predominantly on the -c surface but disappear inside the crystal bulk.

Light-induced removal of 180° ferroelectric domains in Rh:BaTiO_3

“…1. It is exactly the same method used by Grubsky et al to detect 180°domains using photorefractive two-beam coupling, known colloquially as the "Swiss cheese technique" [10]. A photorefractive grating is recorded by interfering two beams inside the photorefractive crystal, a probe beam which is collimated and which propagates parallel to the crystal's c-axis, and a reference beam, which can either enter the crystal through the c-face, as shown in Fig.…”

“…The contrast of these spots will depend on the length of the domains along the c-axis, being maximum when they extend from one c-face to the other. Most domains do [10,11], since this configuration is energetically more favorable; head-to-head domains require free charge to electrically compensate the discontinuity of the spontaneous polarization at the domain wall. However, wedge-shaped domains that end inside the bulk can occur in barium titanate [12,13], and can be detected by using the set-up shown in Fig.…”

“…1b). By focusing the reference beam with a cylindrical lens the domain structure of a slice of the crystal can be analyzed, and by simply translating the reference beam a tomographic image of the domain structure can be obtained [10]. In order to check the quality of rhodium-doped barium titanate crystals, in preparation for another experiment (not relevant to this paper), we set up the "Swiss cheese experiment."…”

“…We checked the distribution of the domains throughout the bulk of the crystal by scanning a tightly focused (100-200 micron thin stripe) reference beam, as described in Ref. [10]. The angle of incidence of the reference beam was kept constant (exterior angle of 65°with respect to the c-axis) as the focused beam was scanned along the aface in 100 micron increments.…”

Optical Second Harmonic Generation Microscopy as a Tool of Material Diagnosis

“…The light with wavelength 532 nm is selected by a spectrometer (18), and the intensity is detected point by point by a photomultiplier tube (19) that is synchronized with incident laser pulses by a lock-in amplifier (20). The sample stage (13) is driven by the combination of stepping motors and piezoactuators (14) displayed by a computer (21). With this microscope we can select the noninterference geometry simply by shutting off the second path to the reference plate.…”