Junichi Kaneshiro

Three-dimensional observations of polar domain structures using a confocal second-harmonic generation interference microscope

The necessary conditions for nondestructive and three-dimensional (3D) observations of inverted polar domain structures using the second-harmonic generation interference microscope (SHGIM) are examined experimentally and theoretically using MgO doped congruent LiNbO3 and periodically poled (PP) MgO doped near stoichiometrical LiNbO3. The results can be explained well by the Boyd and Kleinman theory of strongly focused optical systems. To obtain clear 3D images of domain structures by SHGIM, the sign of the wave number Δk offset of the fundamental and SH waves should be negative and the SHG tensor components d31 should be used for both samples when they are observed with a wavelength of 1064 nm at room temperature. Under these conditions, 3D PP domain structures are clearly revealed by SHGIM. General conditions for the 3D visualization of polar domain structures are discussed for the cases of sum-frequency and difference-frequency generations.

Three-dimensional observations of periodically poled domains in a LiTaO3 quasiphase matching crystal by second harmonic generation tomography

Second harmonic generation interference tomography which enables us to obtain three-dimensional images of ferroelectric antiparallel domain structures is devised. Periodically poled domains (PPDs) inside a LiTaO3 quasiphase matching crystal (QPM) are observed by this microscope. Section images perpendicular to the polar z axis show that the PPD structure is maintained throughout the top quarter of the sample but it starts to lose the periodic nature in the bottom half of the sample. Corresponding degradation of the QPM performance is observed along the z direction of the sample.

Visibility of inverted domain structures using the second harmonic generation microscope: Comparison of interference and non-interference cases

The visibility of inverted domain structures using the second harmonic generation (SHG) microscope is discussed based upon the three-wave coupling equations. Without reference second harmonic (SH) waves (non-interference case), the SHG intensity at a domain boundary decreases steeply along the perpendicular direction to the domain wall, which is observed as a dark line. Thus the non-interference SHG microscope reveals the location of domain boundaries but not the domain polarity which the SHG interference microscope can do. In the case of periodically poled domain structures, the clear observation criterion is expressed with the wave-number offset between the fundamental and SH waves.

Optical Second Harmonic Generation Microscopy as a Tool of Material Diagnosis

The second harmonic generation microscope (SHGM) constructs images of intensity distributions of SH waves produced by the interaction of fundamental waves with a polar material. We have developed this nonlinear optical microscope in order to make possible nondestructive, three-dimensional (3D) observations of various kinds of inorganic and organic materials. The SHGM can disclose also inverted domain structures of antiparallel spontaneous polarizations using the interference with the reference SH waves. The observation principle and several applications to structural characterizations of LiNbO3 and LiTaO3 quasi-phase matching devices, domain structure analyses of a relaxor/ferroelectric solid solution Pb(Zn1/3Nb2/3)O3-9%PbTiO3 at the morphotropic phase boundary, development of order parameter in a quantum paraelectric relaxor Li-doped KTaO3, and antiphase polar domain structures of muscle fibers and myofibrils are surveyed by stressing the high effectiveness of the SHGM as a tool of material diagnosis.

Non-centrosymmetric coordination polymer with a highly hindered octahedral copper center bridged by mandelate.

A novel chiral coordination polymer, [Cu(C(6)H(5)CH(OH)COO)(μ-C(6)H(5)CH(OH)COO)] (1-L and 1-D), was synthesized through a reaction of copper acetate with L-mandelic acid at room temperature. Although previously reported copper mandelate prepared by hydrothermal reaction was a centrosymmetric coordination polymer because of the racemization of mandelic acid, the current coordination polymer shows noncentrosymmetry and a completely different structure from that previously reported. The X-ray crystallography for 1-L revealed that the copper center of the compound showed a highly distorted octahedral structure bridged by a chiral mandelate ligand in the unusual coordination mode to construct a one-dimensional (1D) zigzag chain structure. These 1D chains interdigitated each other to give a layered structure as a result of the formation of multiple aromatic interactions and hydrogen bonds between hydroxyl and carboxylate moieties at mandelate ligands. The coordination polymer 1-L belongs to the noncentrosymmetric space group of C2 to show piezoelectric properties and second harmonic generation (SHG) activity.

Three-Dimensional Observations of LiNbO3 and LiTaO3 Quasi-Phase Matching Devices Using Transmission-Type Scanning Second-Harmonic Generation Interference Microscope

Periodically poled domain structures in stoichiometric LiNbO3 (PPSLN) and LiTaO3 (PPSLT) are observed using an optical second harmonic generation (SHG) interference microscope. Three-dimensional section images can be obtained in PPSLN using d31 SHG tensor component. In PPSLT, the images of top and bottom surfaces are obtained using d22 component. The difference in SHG images with and without interference is discussed.

Domain Structure Analyses of Tetragonal BaTiO

The effects of birefringence on polarization dependences of the second-harmonic generation (SHG) measured with a focused optical system are examined experimentally and theoretically for tetragonal domain structures of ferroelectric BaTiO3. Polar diagram shapes of the SHG intensity are modified owing to the phase difference of mutually perpendicular waves due to birefringence, but no essential change in the spontaneous polarization direction is observed.

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Successive phase transitions of Pb(Zn1/3Nb2/3)O3–9%PbTiO3 single crystals with the morphotropic phase boundary composition are investigated using polarization and scanning-type second-harmonic generation (SHG) microscopes. Clear phase transitions between monoclinic and tetragonal, and tetragonal and cubic phases are observed with temperature hysteresis. A three-dimensional domain structure with a domain boundary consistent with the m3mFm( p) transition is observed with the SHG microscope at room temperature. Monoclinic domains develop with a long relaxation time in the zero-field cooling process.

Single Crystal by Scanning Second-Harmonic Generation Microscopy: Birefringence Effect on Second-Harmonic Generation Polarization Diagram

Necessary conditions for the three-dimensional (3D) observation of polar domain structures using the second harmonic generation (SHG) interference microscope are examined. The essential point for the 3D observation is the use of an SHG tensor component with a negative wave-number misfit parameter Δk(= k2–2k1) between the wave-number k1 of the fundamental wave and k2 of the SH wave. The origin of this phenomenon is explained with the Fourier transform technique. Δk diagrams of the possible 3D observation are obtained for the sum-frequency generations in Mg doped LiNbO3 and BaTiO3.

Optical and Nonlinear Optical Investigations of Phase Transition of Pb(Zn1/3Nb2/3)O3–9%PbTiO3 Single Crystals

Non-destructive and contactless observations of the domain structures in a single crystal of solid solution Pb(Zn1/3Nb2/3)O3–9%PbTiO3 (PZN–9PT) was performed using the scanning second-harmonic generation (SHG) microscopy with the spatial resolution of optical wavelength scale. A novel method of the 2D mapping of SHG polarization dependence (Pol-D) is proposed. The result indicates that the Pol-Ds correspond well to the observed SHG images of domain structures. The directions of ferroelectric spontaneous polarizations are quantitatively analysed by comparing SHG images and the Pol-Ds. It is confirmed that PZN-9PT has the monoclinic symmetry at room temperature.