Recording of domains by an electron beam on the surface of +Z cuts of lithium niobate

Using an electron beam, spontaneous polarization on the surface of +Z cuts of lithium niobate crystals of various compositions is switched. Domains 100–200 nm in size are formed in a thin surface layer, with the thickness dependent on the primary-electron energy. The sizes of segments, on which submicron domains are formed, exceed the sizes of the irradiation region. The distributions of domains on the surface in crystals of various compositions are different and depend on the method of moving the electron beam and irradiation conditions. The results are discussed in the context of notions on the charging of dielectric materials by the electron beam. It is assumed that the spontaneous polarization in the surface layer of +Z cuts of lithium niobates is switched by the field of a double layer of charges formed as a result of the charging process near the surface.     

Periodic domain structures in stoichiometric lithium niobate: Formation by electron beam

The formation of periodic domain structures in stoichiometric lithium niobate crystals via direct surface irradiation using a controllable electron beam in a scanning electron microscope is studied. The periodic domain structures are fabricated at different microscope parameters (current, voltage, charge density) and different ways of charge implantation. The irradiation modes for the formation of uniform periodic domain structures are experimentally found. The use of optimal electron-beam parameters and ways of crystal surface irradiation make it possible to fabricate domain structures with a period of 6.9 μm in a crystal 0.5 mm thick. Domain structures of this kind can be used for optical wavelength conversion by quasi-phase-matching and second harmonic generation in lithium niobate.     

Linear propagation of dust acoustic modes in the presence of an electron beam

The physical and optical properties of plasmas are depended on dynamics of species in the discharge volume. Then, the presence of an electron beam, as a separate component, in a dusty plasma can modify the plasma structures through altering the discharge parameters. In this report, the linear propagation of acoustic modes in a collisionless dusty plasma contains electrons, ions and charged dust grains is investigated in the presence of an electron beam. Our analysis indicates that the electron beam can modify the dispersion relations of dust acoustic modes which resulted different data transportation in dusty plasmas. The obtained results are also examined for negative and positive charged dust grains with different number densities. The charge of dust grains represents an important role in the dynamics of the low frequency waves. Additionally, our findings reveal that the propagation of acoustic waves in dusty plasmas can be controlled by adjusting the electron number density of the beam and the cathode potential. Lastly, we obtian the destabilizing effects, originated from dust charge fluctuation, by reconsidering the dispersion relations of both dust acoustic modes.     

Damage in lithium niobate induced by a high-power proton-carbon beam

Surface damage in lithium niobate LiNbO₃ induced by a high-power proton-carbon beam was investigated. Typical damage patterns were observed. The effect of thin metal surface coating on the damage was considered.     

Effects of surface roughness on surface acoustic wave propagation in semiconductor materials

The effect of surface roughness on adhesion and tribological properties of films and interfaces is of key importance. Therefore, it is of utmost importance to be able to measure this quantity and to predict the effects that different roughness levels may cause. Roughness affects the propagation of surface acoustic waves on a material but there is little useful quantitative data on the topic. This work investigates the dispersive effect of roughness on surface acoustic wavepackets (30-200 MHz frequency range) for different degrees of nanometer roughness on silicon (0 0 1) and (1 1 1) surfaces, we show that the roughness-induced frequency dispersion effect is significant, and that although available theories agree qualitatively with the results, the theory is not adequate to predict the real SAW dispersion. These experimental results have considerable implications for design of SAW devices, for accuracy of Brillouin spectroscopy measurements, and for possible applications to non-destructive testing of materials. Previously unknown dispersive effects on anisotropic crystal surfaces are also demonstrated.     

Kinetics of electron emission from lithium niobate

The kinetics of thermally stimulated electron emission from single-crystal lithium niobate has been studied. The emission current relaxation time is calculated for the temperature range 45–90°C. It is established that an increase in the heating rate brings about a considerable broadening of the temperature range within which emission occurs. The results obtained are treated in terms of the model of field emission from surface states in ferroelectrics.     

FE simulation of laser generated surface acoustic wave propagation in skin

Advances in laser ultrasonics have opened new possibilities in medical applications, such as the characterization of skin properties. This paper describes the development of a multilayered finite element model (FEM) using ANSYS to simulate the propagation of laser generated thermoelastic surface acoustic waves (SAWs) through skin and to generate signals one would expect to observe without causing thermal damage to skin. A transient thermal analysis is developed to simulate the thermal effect of the laser source penetrating into the skin. The results from the thermal analysis are subsequently applied as a load to the structural analysis where the out-of-plane displacement responses are analysed in models with varying dermis layer thickness.     

Light propagation in double-periodic nonlinear photonic lattices in lithium niobate

Single- and double-periodic one-dimensional photonic lattices are formed in lithium niobate using both titanium in-diffusion and holographic grating recording. We investigate linear band structures and diffraction properties of such superlattices and observe a decrease of discrete diffraction with increasing modulation depth of the second superimposed lattice. In weakly modulated superlattices with tailored diffraction properties, our results demonstrate the formation of discrete solitons having a propagation constant inside the extra mini-gap formed inside the Brillouin zone. PACS 42.65.Tg; 42.70.Qs; 42.82.Et     

声表面波介质表面受力条件下的波速变化研究

为了计算力负载直接作用在声表面波传播表面时波速的变化特性,通过有效材料系数将负载引入,并用广义Green函数计算声速,得到了数值计算的结果,并用声表面波谐振器进行了实验.实验结果表明,将力负载直接加载在声表面波的传播表面时,波速变化量和力负载大小近似为线性关系,该加载方式下,实验中声表面波谐振器的谐振频率对外加质量负载有较高的灵敏度,可达1900 Hz/g.     

X-ray diffraction analysis of the surface acoustic wave propagation in langatate crystal

X-ray diffraction on a langatate crystal (La₃Ga_5.5Ta_0.5O₁₄, LGT) modulated by a Λ=12 μm Rayleigh surface acoustic wave (SAW) was studied in a double axis X-ray diffractometer scheme at the BESSY synchrotron radiation source. SAW propagation in the crystal causes sinusoidal modulation of the crystal lattice and the appearance of diffraction satellites on the rocking curves, with their number, angular positions, and intensities depending on the wavelength and amplitude of acoustic vibrations of the crystal lattice. Strong absorption of X-ray radiation in LGT enables the observation of the diffraction spectra extinction at certain SAW amplitudes. X-ray diffraction spectra analysis makes it possible to determine SAW amplitudes and wavelengths, to measure the power flow angles, and investigate the diffraction divergence in acoustic beam in LGT.     

Self-similar surface nanodomain structures induced by laser irradiation in lithium niobate

Self-similar surface structures composed of nanodomain rays, which are formed in congruent lithium niobate single crystals under pulsed laser irradiation, are investigated. The computer simulation of the formation of the domain structure is performed using the experimentally revealed rules of ray growth. It is demonstrated that the domain structures formed are fractal objects with a limited range of scaling.     

SH surface acoustic wave propagation in a cylindrically layered piezomagnetic/piezoelectric structure

SH surface acoustic wave (SH-SAW) propagation in a cylindrically layered magneto-electro-elastic structure is investigated analytically, where a piezomagnetic (or piezoelectric) material layer is bonded to a piezoelectric (or piezomagnetic) substrate. By means of transformation, the governing equations of the coupled waves are reduced to Bessel equation and Laplace equation. The boundary conditions imply that the displacements, shear stresses, electric potential, and electric displacements are continuous across the interface between the layer and the substrate together with the traction free at the surface of the layer. The magneto-electrically open and shorted conditions at cylindrical surface are taken to solve the problem. The phase velocity is numerically calculated for different thickness of the layer and wavenumber for piezomagnetic ceramics CoFe₂O₄ and piezoelectric ceramics BaTiO₃. The effects of magnetic permeability on propagation properties of SH-SAW are discussed in detail. The distributions of displacement, magnetic potential and magneto-electromechanical coupling factor are also figured and discussed.     

On the modulation of an electron beam by the slow light wave

The modulation of an electron beam with a large energy spread at optical frequencies on the basis of the stimulated Cherenkov absorption has been shown to posses an advantage over the Schwarz and Hora method. Two possible realizations of the Cherenkov modulation scheme are proposed.     

Observation of superluminal and slowdown light propagation in doped lithium niobate crystals

We investigate the group velocity of light in a one-dimensional volume grating inside lithium niobate crystals doped with different impurities. The superluminal and slowdown light propagations are both observed in the crystals. The relationships between the group refractive index and the grating amplitude and phase shift are presented and discussed.     

Two-dimensional acoustic wave propagation in elastic ducts

Integral transforms are employed in order to obtain a formal solution to the two-dimensional elastic-walled duct problem. The fluid inside the duct is stationary, inviscid and compressible, and is identical to the fluid outside the duct. A time-harmonic line source lies between the duct walls. With attention confined to the field inside the duct, an asymptotic analysis is implemented for high and low frequencies, yielding residues which are valid throughout the duct and branch-cut contributions which apply only in the far field.     

Nonlinear response of photorefractive lithium tantalate and niobate at acoustic frequencies

An amplification of the intensity of pump oscillations is observed experimentally at frequencies from 100 Hz to 1 kHz during photoinduced light scattering and holographic-type parametric scattering in photorefractive lithium tantalate and niobate. Possible ways are analyzed for explaining the existence of a photorefractive response in these crystals over times of 10⁻²–10⁻³ s, which are five orders of magnitude shorter than the Maxwell time. Zh. éksp. Teor. Fiz. 112, 1490–1498 (October 1997)     

Anisotropic effects in surface acoustic wave propagation from a point source in a crystal

Strong anisotropic effects in the propagation of surface acoustic waves (SAWs) from a point-like source are studied experimentally and theoretically. Nanosecond SAW pulses are generated by focused laser pulses and detected with a cw probe laser beam at a large distance from the source compared to the SAW wavelength, which allows us to resolve fine intricate features in SAW wavefronts. In our theoretical model, we represent the laser excitation by a localized impulsive force acting on the sample surface and calculate the far-field surface response of an elastically anisotropic solid to such a force. The model simulates the measured SAW waveforms very well and accounts for all experimentally observed features. Using the data obtained for the (111) and (001) surfaces of GaAs, we describe a variety of effects encountered in the SAW propagation from a point source in crystals. The most interesting phenomenon is the existence of cuspidal structures in SAW wavefronts resulting in multiple SAW arrivals for certain ranges of the observation angle. Cuspidal edges correspond to the phonon focusing directions yielding sharp peaks in the SAW amplitude. A finite SAW wavelength results in internal diffraction whereby the SAW wavefront spreads beyond the group velocity cusps. Degeneration of a SAW into a transverse bulk wave is another strong effect influencing the anisotropy of the SAW amplitude and making whole sections of the SAW wavefront including some phonon focusing directions unobservable in the experiment. The propagation of a leaky SAW mode (pseudo-SAW) is affected by a specific additional effect i.e. anisotropic attenuation. We also demonstrate that many of the discussed features are reproduced in powder patterns, a simple technique developed by us earlier for visualization of SAW amplitude anisotropy.Received: 17 June 2003, Published online: 15 October 2003PACS: 43.35.+d Ultrasonics, quantum acoustics, and physical effects of sound - 68.35.Gy Mechanical properties; surface strains - 62.65.+k Acoustical properties of solidsA.M. Lomonosov: On leave from the General Physics Institute, 117942 Moscow, Russia