Ultrashort optical pulse in a defect order-disorder ferroelectric

Physics of the Solid State - The dynamics of an ultrashort optical pulse in order—disorder ferroelectrics in the presence of defects without limitations on the pulse power is considered in...     

Nondestructive remote imaging of ferroelectric domain distributions with high three-dimensional resolution

The domain distribution in the bulk and at the surface of ferroelectric crystals is imaged by second-harmonic microscopy with three-dimensional far-field optical resolution. The nondestructive technique allows us to investigate the success of a poling procedure in a fabrication state of an integrated optical device in which the poling electrodes have not been removed. Additionally, a confocal linear optical imaging technique is introduced, which reveals the surface topography with ±0.7 nm height sensitivity. At the surface of a periodically poled specimen, we detect unexpected and unwanted surface topographies that correspond to the domain structure. The search for improved fabrication parameters that guarantee smooth surfaces could be substantially promoted with our topography-detection technique. Received: 16 May 2001 / Published online: 23 October 2001     

Permissible domain walls in ferroelectric species

A previously developed method makes it possible to determine the orientations of domain walls in ferroelectrics which are permissible under the condition that neighbouring domains must be mechanically compatible. In this paper, the method has been applied to all 88 ferroelectric species in which the polarization is the parameter of the transition. Types of permissible walls and their orientations are listed in form of tables. Cases where no walls fulfil the compatibility conditions are shown.     

Ultrashort pulse characterization with a terahertz streak camera

A phase-locked terahertz transient is exploited as an ultrafast phase gate for femtosecond optical pulses. We directly map out the group delay dispersion of a low-power near-infrared pulse by measuring the electro-optically induced polarization rotation as a function of wavelength. Our experiment covers the spectral window from 1.0 to 1.4 μm and reaches a temporal precision better than 1 fs. A quantitative analysis of the detector response confirms that this streaking technique requires no reconstruction algorithm and is also well suited for the characterization of pulses spanning more than one optical octave.     

Stress-induced phase transition in ferroelectric domain walls of BaTiO3

The seminal paper by Zhirnov (1958 Zh. Eksp. Teor. Fiz. 35 1175-80) explained why the structure of domain walls in ferroelectrics and ferromagnets is drastically different. Here we show that the antiparallel ferroelectric walls in rhombohedral ferroelectric BaTiO(3) can be switched between the Ising-like state (typical for ferroelectrics) and a Bloch-like state (unusual for ferroelectric walls but typical for magnetic ones). Phase-field simulations using a Ginzburg-Landau-Devonshire model suggest that this symmetry-breaking transition can be induced by a compressive epitaxial stress. The strain-tunable chiral properties of these domain walls promise a range of novel phenomena in epitaxial ferroelectric thin films.     

Depletion layers and domain walls in semiconducting ferroelectric thin films

Commonly used ferroelectric perovskites are also wide-band-gap semiconductors. In such materials, the polarization and the space-charge distribution are intimately coupled, and this Letter studies them simultaneously with no a priori ansatz on either. In particular, we study the structure of domain walls and the depletion layers that form at the metal-ferroelectric interfaces. We find the coupling between polarization and space charges leads to the formation of charge double layers at the 90 degrees domain walls, which, like the depletion layers, are also decorated by defects like oxygen vacancies. In contrast, the 180 degrees domain walls do not interact with the defects or space charges. Implications of these results to domain switching and fatigue in ferroelectric devices are discussed.     

Charge contrast of ferroelectric domain walls in ferroelastic terbium molybdate

An extraordinary potential contrast of a plane domain wall forming in the case of excess negative charging of a ferroelastic-ferroelectric Tb₂(MoO₄)₃ sample with a two-domain structure has been detected using a scanning electron microscope. Conditions and features of the formation of this potential contrast (called charge contrast) in the domain wall region are determined. It is shown that the surface is charged at a lower rate in the domain wall region, which is an elastically strained crystal region. The smallest domain wall width determined by the charge-contrast image was 1.6 μm on the average.     

Mode dependent scattering of phonons by domain walls in ferroelectric KDP

Thermal conductivity and ballistic phonon imaging measurements in KH₂PO₄ (KDP) at low temperature (T<3K) indicate that scattering from domain walls has a large effect on phonon transport. kDP has a ferroelectric phase transition from tetragonal to orthorhombic structure atT _c =122 K. BelowT _c domains of opposite electric polarization and crystal orientation form unless the sample is colled in an electric field. Thermal conductivity measured along the [100] (tetragonal) axis drops 30% when domain walls are present, which is independent of sample size and temperature. We attribute this decrease to phonon polarization-dependent scattering at the domain boundaries. This is verified by measurements of ballistic transport, using phonon imaging techniques, which reveal the phonon polarization and mode dependence of the scattering. The scattering is successfully modelled using continuum acoustics with simple acoustic mismatch at the domainwall. The interface scattering is found to be mode dependent: Caustic structures in the phonon images due to slow transverse phonons are most affected by the domain wall scattering, which channels these phonons along parallel planes by multiple reflections without mode conversion. Mode conversion scattering, though possible for a number of phonons, has little effect on the overall phonon transmission.     

Ultrashort optical pulse in an order-disorder ferroelectric in the presence of a lattice of defects

The dynamics of an ultrashort optical pulse in an order-disorder ferroelectric in the presence of a lattice of defects is considered within the microscopic pseudospin formalism in the unidirectional propagation approximation, without limitations on the pulse power. The effective equations for the electric field amplitude and ferroelectric polarization are obtained and numerically solved. Quasi-soliton modes of ultrashort optical pulse propagation in a system with regular defects are revealed and the dependences on the microscopic Hamiltonian parameters are analyzed. The effect of the parameters of defects of different types on the pulse propagation is revealed.     

Equations for domain walls in a coordinate system of the ferroelectric phase

Two methods are suggested for writing equations for domain walls in a coordinate system of the ferroelectric phase in ferroelastics and multiaxial ferroelectrics. The equations for domain walls in ferroelectric barium titanate and ferroelastic lead orthophosphate are derived. It is shown that suborientation states are possible in these crystals. The suggested methods make it possible to find the matrices of the transformation from the coordinate system of the paraelectric phase to a coordinate system of the ferroelectric phase for each orientation state.     

Operating mode of high pressure straws with high spatial resolution

The article presents results of studying the operating mode of thin-walled drift tubes (straws) at flushing it with a high-pressure gas mixture, which allowed obtaining extremely high spatial resolution for straw detectors. The results of studying the radiation ageing of straws operating in this mode are also described.     

The miniature light-field camera with high spatial resolution

Optical Review - A light-field camera is an optical system that provides multi-field-angle information in one shot. The microlens array (MLA) in a light-field camera system is the key to provide...     

Highly sensitive, single-shot characterization for pulse widths from 0.4 to 85 ps using electro-optic shearing interferometry

Single-shot characterization using electro-optic shearing interferometry (EOSI) is shown for pulse widths ranging from their transform limit (0.4 ps) to 200x their limit (85 ps). In EOSI, the spectral phase is reconstructed by interfering two spectrally sheared replicas of the pulse under test, where the shear is produced by applying linear temporal-phase modulation. We present a new reconstruction algorithm for accurately characterizing chirped pulses, even if the pulse extends beyond the linear region of the phase modulation. Furthermore, since EOSI does not rely on nonlinear optical processes, it requires only 1 nJ pulse energies for all pulse widths, corresponding to a single-shot sensitivity 1000x higher than previously demonstrated.     

Crystallographic orientation dependence of ferroelectric domain walls in antiferroelectric lead zirconate thin films

Domains of antiferroelectric PbZrO₃ have been studied. The (111) PbZrO₃ has lower field transitions due to the reduction of the angle between the ferroelectric polar axis and the applied electric field. The study of the permittivity reveals also that the (111) PbZrO₃ has a higher correlation of dipoles (|S_hf| = 0.007) due to the energy gain associated with their orientation. Therefore, the (111) crystallographic orientation is a better choice for obtaining easily switching domain. The dielectric response of the domain walls in the (100) and (111) PbZrO₃ are identical because they have the same environment (same grain size and similar defects) and interact in the same way. Only the domain wall density is higher in the (111) PbZrO₃ due to its lower crystallographic orientation factor. Different crystallographic directions have more obstacles due to the inhomogeneity of the crystallization and consequently has more nucleation site for domain walls.     

In-duct identification of fluid-borne source with high spatial resolution

Source identification of acoustic characteristics of in-duct fluid machinery is required for coping with the fluid-borne noise. By knowing the acoustic pressure and particle velocity field at the source plane in detail, the sound generation mechanism of a fluid machine can be understood. The identified spatial distribution of the strength of major radiators would be useful for the low noise design. Conventional methods for measuring the source in a wide duct have not been very helpful in investigating the source properties in detail because their spatial resolution is improper for the design purpose. In this work, an inverse method to estimate the source parameters with a high spatial resolution is studied. The theoretical formulation including the evanescent modes and near-field measurement data is given for a wide duct. After validating the proposed method to a duct excited by an acoustic driver, an experiment on a duct system driven by an air blower is conducted in the presence of flow. A convergence test for the evanescent modes is performed to find the necessary number of modes to regenerate the measured pressure field precisely. By using the converged modal amplitudes, very-close near-field pressure to the source is regenerated and compared with the measured pressure, and the maximum error was −16.3 dB. The source parameters are restored from the converged modal amplitudes. Then, the distribution of source parameters on the driver and the blower is clearly revealed with a high spatial resolution for kR<1.84 in which range only plane waves can propagate to far field in a duct. Measurement using a flush mounted sensor array is discussed, and the removal of pure radial modes in the modeling is suggested.     

Broad-band NMR with a high spectral and spatial resolution

Spatially selective excitation sequence CARVE (completely arbitrary regional volume excitation) excites signal from an arbitrarily shaped profile (I. Sersa, S. Macura: Magn. Reson. Med.37, 920–931, 1997) by an interleaved sequence of precalculated small tip angle radio-frequency pulses and gradient pulses. Here we propose a spatially selective observation method based on the CARVE principles which is insensitive to the relaxation and the off-resonance effects. The method, CARVED (CARVE detection), excites spins uniformly across the sample and across the spectrum but achieves spatial selectivity by weighted coaddition of the signals after the data acquisition. CARVE-D is suitable for spatially selective high-resolution nuclear magnetic resonance spectroscopy in chemically and geometrically complex systems. The method is analyzed theoretically and demonstrated experimentally on model systems.     

Reflection of electroacoustic waves from a system of moving domain walls in a ferroelectric

The interaction of electroacoustic waves with a periodic domain structure formed in a tetragonal ferroelectric by a finite number of uniformly moving 180° domain walls is considered in the quasi-static approximation. It is established that the inclusion of the domain-wall motion leads to a significant modification of the reflectance spectra of electroacoustic waves according to the number, intensity, and location of the Bragg reflectance peaks.