External Dc Electric Field Research Articles

Electric-Field-Induced Symmetry Breaking of Angular Momentum Distribution in Atoms

We report the experimental observation of alignment to orientation conversion in the 7D3/2 and 9D3/2 states of Cs in the presence of an external dc electric field and without the influence of magnetic fields or atomic collisions. Initial alignment of angular momentum states was created by two-step excitation with linearly polarized laser radiation. The appearance of transverse orientation of angular momentum was confirmed by the observation of circularly polarized light. We present experimentally measured signals and compare them with the results of a detailed theoretical model based on the optical Bloch equations. The effect is odd under time reversal and should be taken into account in ever more sensitive searches for an electron electric dipole moment.

Switching of Electrically Commanded Alignment Layers Probed by Optical Second Harmonic Generation

Optical second harmonic generation (SHG) was used to probe the response of a 200 nm thick electrically commanded alignment layer made of ferroelectric liquid crystal polymer (FLCP) film to an external DC electric field. The results show that for the field magnitudes in the range 0–2 V/μm the field induced reorientation effects represent only a relatively minor structural perturbation of the film. The switching process is monostable and shows characteristics of the “V-shaped” switching. The response time of the SHG signal is relatively longer than what is measured for the bulk FLCP. Several mechanisms are considered as possible reasons for that.

Electric field induced hyperfine level-crossings in (nD)Cs at two-step laser excitation: Experiment and theory

The pure electric field level-crossing of mF Zeeman sublevels of hyperfine F levels at two-step laser excitation is described theoretically and studied experimentally for the nD3/2 states in Cs with n=7, 9 and 10, by applying a diode laser in the first 6S1/2→6P3/2 step and a diode or dye laser for the second 6P3/2→nD3/2 step. Level-crossing resonance signals are observed in the nD3/2→6P1/2 fluorescence. A theoretical model is presented to describe quantitatively the resonance signals by correlation analysis of the optical Bloch equations in the case when an atom simultaneously interacts with two laser fields in the presence of an external dc electric field. The simulations describe well the experimental signals. The tensor polarizabilities α2 (in a03) are determined to be 7.45(20)×104 for the 7D3/2 state and 1.183(35)×106 for the 9D3/2 state; the electric field calibration is based on measurements of the 10D3/2 state, for which α2 is well established. The α2 value for the 7D3/2 state differs by ca. 15% from the existing experimentally measured value.

New mechanism of formation of virtual surface magnetic polaritons

By using an easy-axis antiferromagnetic material as an example, the conditions are found under the fulfillment of which, the quadratic magneto-optical interaction in an external dc electric field perpendicular to the easy axis gives rise to the formation of a new type of virtual surface magnetic TM polaritons at the interface both between an antiferromagnet and an ideal metal and between an antiferromagnet and vacuum.

The Characterization of Two Dimensional Electrostrictive CuInP<sub>2</sub>S<sub>6</sub> Materials for Transducers

The electromechanical properties of layered, two-dimensional materials of CuInP2S6 family have been investigated. It was shown that, at room temperature, which is above phase transition and under DC bias electric field, these materials behave as a piezoelectric because of electrostriction. In this case, the piezoelectric and electromechanical coupling coefficients are odd functions of the bias field and have a linear dependence on the bias field. The relative changes of ultrasonic velocity are found to have a quadratic dependence on the bias DC field. In bias fields of about 20 kV/m, the values of square of electromechanical coupling coefficient could be high enough (>20%) for longitudinal vibrations in thin plates of investigated CuInP2(S,Se)6 materials in the paraelectric phase. In the ferroelectric phase, the external DC electric field acts as polarizing field and electromechanical coupling coefficients sufficiently increase. At the transitions, the piezoelectric anomalies have been observed.

Influence of an applied electric field on the torque of rotary lip seals on metal shafts. Part I: Effects of lip seal type

The paper presents some results of experiments on the tribocharging of selected engine oil and on the effect of an auxiliary external DC electric field on the work of machines which contain rotating parts such as shafts, crankshafts, etc. The research was especially aimed at the braking torque of a rotating metal shaft sealed with a lip seal and a possibility of reduction in the torque under external DC electric fields. DC voltage was applied between the stiffening ring of four different lip seals under test and a rotating, earthed shaft in a metal shaft-oil film-lip seal system. The relationships of the torque to the voltage of positive and negative polarities were established on the basis of measurements of the torque under steady-state conditions for a constant oil temperature and given different angular shaft velocities. In general, it was found that positive and negative DC electric fields produce adverse effects on the torque depending on the type of oils and on the material of which the lip seals were made. In only one case, the torque decreased with the increasing absolute value of the negative voltage applied.

Influence of an applied electric field on the torque of rotary lip seals on metal shafts. Part II: Effects of oil type

The experimental results are presented of research on the tribocharging of selected engine oils and on the effect of an auxiliary external DC electric field on the work of rotary machinery. There exists an effect of the type of oil, its temperature, and the electric field on the braking torque of rotating parts such as shafts, crankshafts, etc. sealed with lip seals. The research was especially aimed at the possibility of reduction in the torque under external electric fields for different engine oils. To obtain the auxiliary electric field the DC voltage was applied between the stiffening ring of a fluorocarbon lip seal and the rotating, earthed shaft in the metal shaft–oil film–lip seal system. The measurements of the torque were performed under steady state conditions for given different oil temperatures, angular shaft velocities, and voltages; also three different oils were used. It was found that for the lip seal under test the negative voltage applied produced a beneficial effect on the torque depending on the type of oils.

Effects of an electric field applied during the solution heat treatment of the Al–Mg–Si–Cu alloy AA 6111 on the subsequent natural aging kinetics and tensile properties

Abstract The effects of an external dc electric field of 0–5 kV/cm, applied at 475–550°C during solution heat treatment (SHT) to AA6111, on the subsequent natural aging kinetics and volume fraction of precipitated clusters were determined employing resistivity. The field increased the as-quenched resistivity and that during natural aging, the effect being significant from 0 to ≈0.5 kV/cm and increasing only slightly, if at all, thereafter. An Avrami-type analysis of the natural aging kinetics gave n = 0.59 ± 0.2 and k = (1.2 ± 0.8) · 10−2 min−1, relatively independent of SHT temperature and field strength. The field increased the volume fraction of precipitated clusters which occurred during natural aging. This was attributed to the increase in solubility during SHT produced by the field. Tensile properties equivalent to those obtained by the SHT at 550°C without a field were obtained at 500°C with a field of only 200 V/cm, representing a reduction of 50°C in the nominal SHT temperature.

The influence of incompatibility and dielectric contrast on the electric field-induced orientation of lamellar block copolymers

We investigate the influence of incompatibility and dielectric contrast on the reorientation kinetics of concentrated solutions of lamellar block copolymers in the presence of an external DC electric field. We study solutions of AC diblock copolymer and ABC triblock terpolymers. The inclusion of a short, polar middle block B is used to tailor both the degree of incompatibility and the dielectric contrast between the two majority phases. In situ synchrotron radiation small-angle X-ray scattering is used to monitor the reorientation process. For the AC diblock copolymer sample only weak electric field induced reorientation could be achieved, following a very slow kinetics, whereas for the ABC triblock terpolymer, reorientation is observed above a threshold value of 0.3 kV/mm. The orientation kinetics is well described by a single exponential with characteristic time constants varying between a few seconds and several minutes depending on the polymer concentration and the electric field strength. We identify a narrow concentration window, in which the interplay between chain mobility and gain in free energy in the electric field allows the preparation of highly anisotropic bulk polymer samples by exposure to an electric field. The results are compared to free energy calculations revealing a distinct difference in the driving force for reorientation as a consequence of an increase in dielectric contrast and chain mobility upon introduction of the B middle block.

Wave coupling theory of the linear electro-optic effect in a linear absorbent medium

We develop a wave-coupling theory of the linear electro-optic effect, which includes linear absorption of the electro-optic medium. A general solution of the output complex amplitudes of two independent polarized components of a light wave is obtained for a light wave propagating along any direction with an external dc electric field along an arbitrary direction in any linear absorbent electro-optic medium. We use a LiNbO3 crystal as an example for studying the influences of linear absorption on the phases and amplitudes of the two wave components as well as the half-wave voltage and the extinction ratio of electro-optic modulation. © 2005 Optical Society of America.

Multi-layer structure of mid-latitude sporadic-<i>E</i> observed during the SEEK-2 campaign

Abstract. In the mid-latitude ionospheric region, sporadic-E layers (Es layers) have often been observed, revealing multiple layers. The Es layers observed during the SEEK-2 rocket campaign showed double electron density peaks; namely, there are stable lower peaks and relatively unstable upper peaks. We examined the effects of wind shear and the electric fields on the generation of the multiple layer structure, in comparison with the electron density profile, the neutral wind, and the DC electric field observed by the S310 rocket experiments. The results showed that the neutral wind shear is mainly responsible for the generation of the lower layer, while the DC electric field makes a significant contribution to the formation of the upper layer. The difference between the lower and upper layers was also explained by the enhanced AC electric field observed at about 103–105 km altitude. The external DC electric field intensity is expected to be ~5 mV/m, which is enough to contribute to generate the Es layers in the ionosphere. Keywords. Ionosphere (Electric fields; Ionospheric irregularities, Mid-latitude ionosphere)

Nonlinear suppression of relaxation in dynamic localization phenomenon in a double quantum dot

The role of decoherence in controllable electron dynamics in a double quantum dot, influenced by external ac and dc electric fields, has been analyzed. Using the quasienergy formalism we have obtained the reduced density matrix of the electron subsystem and found the time evolution of the occupation probabilities in each quantum dot. It was shown that the dissipation caused by the phonon environment disappears under certain relations between electric field parameters. In this case one may perform a dynamic localization and form stable electron states localized within one of the dots. The suppression of dissipation is essentially a nonlinear effect, which is possible only in strong electric fields.

Effect of electro-optic modulation on coupled quasi-phase-matched frequency conversion

The electro-optic effect can be employed to modulate the refractive index of an optical superlattice. In coupled quasi-phase matched processes, this modulation will introduce quasi-phase mismatches and result in energy redistribution among the optical waves. Numerical results indicate that an efficient third harmonic in a periodic or quasi-periodic superlattice can be achieved by varying the external dc electric field. This method provides a simple and convenient way to control the efficiencies of frequency conversion.

Cascaded frequency doubling and electro-optic coupling in a single optical superlattice

Frequency doubling and electro-optic (EO) coupling are cascaded in a single optical superlattice due to simultaneous modulation of nonlinear and EO coefficients. The coupling equations are deduced and analyzed, and simulations in both periodic and quasi-periodic structures are presented. The results show that both polarization and magnitude of the second harmonic can be manipulated by an external DC electric field, which is useful when simultaneous frequency conversion and signal tuning are desired.

Tribocharging in a rotating shaft–oil–seal system and the effect of an external electric field

The results are shown of tests on the effect of an auxiliary external DC electric field on the braking torque of a rotating shaft. Experiments were carried out on a simplified model of an engine in whose interior a metal shaft rotated with given angular velocities. The shaft was lubricated with different oils producing an oil film between the shaft's surface and a lip seal. The influence of different oil temperatures on the braking torque was also examined. The results are presented here for fresh Polish oil LOTOS 15W40 and a lip seal diameter of 88 mm. An increase in the negative DC voltage applied between the shaft and stiffening ring of the lip seal caused a reduction in braking torque.

Electric field-induced localization of the magnetic TM polariton near the surface of a magnetically ordered crystal

The necessary conditions are found for which an external dc electric field leads to the formation of a surface TM polariton near the interface between an antiferromagnetic material and a nonmagnetic medium even in the collinear phase of the antiferromagnetic crystal.

Effect of external electric field on the microstructural evolution of La2O3-doped BaTiO3ceramics

Abstract The grain growth behavior of La-doped BaTiO3 specimens was investigated at 1350 °C under DC external electric field. In air atmosphere, grain growth was enhanced at the positive-biased region for the 0.15 mol% La-doped and 0.3 mol% La-doped specimens, while it was enhanced at the negative-biased region for the 1.0 mol% La-doped specimen. For the 0.6 mol% La-doped specimen, on the other hand, both positive- and negative-biased regions showed the same grain size. The demarcation donor composition (0.6 mol% La) shifted to a higher donor concentration when the specimen was heat-treated in nitrogen. The results were explained in terms of the grain boundary potential and its variation with donor concentration, oxygen partial pressure, and defect polarization.

Transient analysis of electro-osmotic secondary flow induced by dc or ac electric field in a curved rectangular microchannel

This study investigates transient secondary flow in a rectangular curved microchannel in which the fluid is driven by the application of an external dc or ac electric field. The resultant flow field evolutions within the microchannel are simulated using the backwards Euler time stepping numerical method in order to clarify the relationship between the changes in the transverse flow field conditions and the intensity of the applied electric field. The transient secondary flow evolutions provide evidence of the growth and decay of vortices in the transverse section. As the applied dc or ac electric field intensity is activated, a small vortex appears in each corner of the microchannel. Both upper and lower corner vortices gradually grow in size and strength and finally merge to form a single vortex, which compresses the original recirculation in the upper and lower half of the transverse section. In this study, the formation of these vortices is investigated through total applied force per unit area existing in the flow. The velocity magnitude of the vortices can be as high as 15% of the core axial speed.

Relaxation phenomena in TlGa0.99Fe0.01Se2 single crystals

The relaxation electronic phenomena occurring in TlGa0.99Fe0.01Se2 single crystals in an external dc electric field are investigated. It is established that these phenomena are caused by electric charges accumulated in the single crystals. The charge relaxation at different electric field strengths and temperatures, the hysteresis of the current-voltage characteristic, and the electric charge accumulated in the TlGa0.99Fe0.01Se2 single crystals are consistent with the relay-race mechanism of transfer of a charge generated at deep-lying energy levels in the band gap due to the injection of charge carriers from the electric contact into the crystal. The parameters characterizing the electronic phenomena observed in the TlGa0.99Fe0.01Se2 single crystals are determined to be as follows: the effective mobility of charge carriers transferred by deep-lying centers μf=5.6×10−2 cm2/(V s) at 300 K and the activation energy of charge transfer ΔE=0.54 eV, the contact capacitance of the sample C c =5×10−8 F, the localization length of charge carriers in the crystal d c =1.17×10−6 cm, the electric charge time constant of the contact τ=15 s, the time a charge carrier takes to travel through the sample t t =1.8×10−3 s, and the activation energy of traps responsible for charge relaxation ΔE σ = ΔE Q = 0.58 eV.

External electric field applied during solution heat treatment of the Al-Mg-Si alloy AA6022

The application of an external dc electric field E = 5 kV/cm during the solution heat treatment (SHT) of AA6022 at 475–552°C increased the as-quenched resistivity. An increase continued throughout subsequent natural aging, and there occurred an increase in the tensile properties for the T4 temper. The increase in yield and tensile strength produced by the electric field applied during the SHT is equivalent to a reduction of 10–25°C in the SHT temperature. A thermodynamic analysis of the results indicated that the field reduced both the enthalpy ΔHs and entropy ΔSs of solution, giving a reduction in Gibbs free energy ΔGs, and in turn an increase in solubility of the alloying constituents.