Presence Of Static Electric Field Research Articles

Temporal instability of a viscous liquid film on an oscillating plane in the presence of static electric field

This work examined the linear instability of a two-dimensional liquid film on an oscillating plane theoretically in the presence of a static electric field perpendicular to the plane. The liquid was considered to be viscous and perfectly conducting, while the gas was considered to be viscous and dielectric. The viscous potential theory and Floquet theory were adopted to obtain the dispersion equation. The influences of electric field intensity, forcing amplitude, forcing frequency, and viscosity were obtained. The results showed that with there is more than one instability region with a non-zero forcing amplitude. The first instability region is called inherent instability, which is due to the electric force overcoming the viscous dissipation, surface tension, and gravity, while the other regions are due to the parametric instability induced by the oscillating plane, forming famous Faraday waves. It was found that increasing the forcing amplitude stabilizes the inherent instability but has a destabilizing impact on Faraday waves. In addition, the increase in the electric field intensity and forcing frequency enhances the inherent instability but has a complex impact on the Faraday waves, depending on the intensity of the viscous dissipation, which is approximately proportional to the square of the wavenumber.

High Harmonic Generation from Oriented Asymmetric Molecules in the Presence of Static Electric Field

Abstract We investigate the high harmonic generation during the interaction of the femtosecond laser field with oriented asymmetric diatomic molecules in the presence of an external static electric field. Based on the numerical solution of the time-dependent Schrödinger equation for the model one-electron system, we calculate the high harmonic generation spectrum for a wide range of static-field strengths. The possibilities for visualizing low-frequency (terahertz and mid-infrared) radiation using time-delay measurements of even high harmonics intensities are discussed.

The Effects of the Ionic Field Strength of Be2+, Mg2+, and Ca2+ and a Static Electric Field (SEF) on the Interaction Between Prothionamide and B12P12 Nanocage: A DFT and TD-DFT Study

In the present study, the capability of B12P12 nanocage to detect and deliver prothionamide (PA) drug in the presence of static electric field (SEF=0.005 to SEF=0.075 a.u.) and Be+2, Mg+2 ,and Ca+2 ions encapsulated inside B12P12 nanocage are investigated at cam-B3LYP/ 6-31G (d, p) level of theory by using Gaussian 09 package. The electrical, quantum, thermodynamic parameters, QTAIM (The quantum theory of atoms in molecules), UV-visible, IR spectra, and RDG (Reduced density gradient) of all considered systems are calculated. The AIM, RDG, LOL (Localized orbital locator) and ELF (Electron localization function) results show that the type of bonding between the drug and the nanocage is a sigma bond and electrostatic. The Be+2 ion has the greatest effect on the electrical behavior of nanocage and increases the conductivity, activity, and electron affinity of nanocage, which is very important in the interaction of nanocage with drugs. The Eads, ΔG and ΔH values of PA drug adsorption on the surface of Be+2@B12P12 nanocage are more than other models. The calculation results show that the static electric field does not play a significant role in the conductivity properties of nanocage and the preparation of a suitable drug sensor.

Observation of blackbody radiation enhanced superradiance in ultracold Rydberg gases

An ensemble of excited atoms can synchronize emission of light collectively in a process known as superradiance when its characteristic size is smaller than the wavelength of emitted photons. The underlying superradiance depends strongly on electromagnetic (photon) fields surrounding the atomic ensemble. High mode densities of microwave photons from 300 K blackbody radiation (BBR) significantly enhance decay rates of Rydberg states to neighbouring states, enabling superradiance that is not possible with bare vacuum induced spontaneous decay. Here we report observations of the superradiance of ultracold Rydberg atoms embedded in a bath of room-temperature photons. The temporal evolution of the Rydberg |nD⟩ to |(n + 1)P⟩ superradiant decay of Cs atoms (n the principal quantum number) is measured directly in free space. Theoretical simulations confirm the BBR enhanced superradiance in large Rydberg ensembles. We demonstrate that the van der Waals interactions between Rydberg atoms change the superradiant dynamics and modify the scaling of the superradiance. In the presence of static electric fields, we find that the superradiance becomes slow, potentially due to many-body interaction induced dephasing. Our study provides insights into many-body dynamics of interacting atoms coupled to thermal BBR, and might open a route to the design of blackbody thermometry at microwave frequencies via collective, dissipative photon-atom interactions.

Resonant terahertz generation from laser filaments in the presence of static electric field in a magnetized collisional plasma

A new scheme of terahertz (THz) generation from laser filaments in plasma in the presence of static electric and magnetic fields is proposed. Two femtosecond laser pulses of different frequencies ( $$\omega_{1} ,\omega_{2}$$ ) and wave numbers ( $$k_{1} ,k_{2}$$ ) are co-propagating under the action of filamentation in a magnetized collisional plasma. THz wave is generated due to the nonlinear coupling between nonlinear velocity and electron density in magnetized collisional plasma. For suitable laser and plasma parameters, the nonlinear coupling results in enhanced nonlinear current density which leads to resonant THz waves. The external D.C. electric and magnetic fields are applied perpendicular to each other and mutually perpendicular to the direction of co-propagating lasers. We have obtained the expression of a dielectric tensor with anisotropic nature, and it is found very useful in the study of THz generation. The applied magnetic field also aids to enhance the transverse components of nonlinear current. This nonlinear current is responsible to generate enhanced terahertz waves at frequency ( $$\omega_{1} - \omega_{2}$$ ). We have found that the normalized THz amplitude increases significantly with the increase in applied D.C. electric field from 10 to 30 kV/cm and magnetic field from 10 to 50kG. Our scheme with numerical analysis may open the door for efficient and cost-effective way to generate THz radiation.

Electric field assisted alignment of monoatomic carbon chains

We stabilize monoatomic carbon chains in water by attaching them to gold nanoparticles (NPs) by means of the laser ablation process. Resulting nanoobjects represent pairs of NPs connected by multiple straight carbon chains of several nanometer lengths. If NPs at the opposite ends of a chain differ in size, the structure acquires a dipole moment due to the difference in work functions of the two NPs. We take advantage of the dipole polarisation of carbon chains for ordering them by the external electric field. We deposit them on a glass substrate by the sputtering method in the presence of static electric fields of magnitudes up to 105 V/m. The formation of one-dimensional carbyne quasi-crystals deposited on a substrate is evidenced by high-resolution TEM and X-ray diffraction measurements. The original kinetic model describing the dynamics of ballistically flowing nano-dipoles reproduces the experimental diagram of orientation of the deposited chains.

Production of Terahertz Radiations by Short Pulse Lasers

In this paper, we develop an analytical formalism for THz generation from Laser filaments in the presence of static electric field in the magnetized collisional plasma. Two femtosecond laser pulses with different frequencies undergo filamentation in magnetized collisional plasma to have non-linear coupling in the presence of transverse static electric field. This results in balancing action of static ponderomotive force with pressure gradient force and forms transverse density ripple and non-linear ponderomotive force couple with density ripple to provide strong non-linear transverse current which results in excitation of THz Radiations at resonance. This coupling is further enhanced by electric static field.

Evaluation of the static electric field effects on freezing parameters of some food systems

In present study the effect of freezing in the absence and presence of static electric field (SEF) on selected freezing parameters of liquid and solid food including: distilled water, NaCl solutions, mushroom extract and mushroom were investigated. The static electric field was applied at the intensities of 0.0–9.6 × 105 V/m during freezing at -30 ± 1 °C. The freezing parameters of different samples were evaluated from the freezing curve of them. Results showed that among the different samples, the pure water had the highest freezing temperature, supercooling degree and shortest phase transition period in the absence of electric field. By applying the electric field, the nucleation temperature and phase transition period of the samples increased. The highest nucleation temperature was observed in the pure water under 6.4 × 105 V/m electric field. The nucleation temperature of the other samples showed an optimum value in the intensity of 3.2 × 105 V/m.

Crack Patterns in Drying Laponite-NaCl Suspension: Role of the Substrate and a Static Electric Field.

We report the formation of crack patterns in drying films of Laponite-NaCl solution. Crack patterns that develop upon drying aqueous Laponite-NaCl solution change drastically as the amount of NaCl is varied in the solution. In this work, we have investigated the effect of NaCl on drying films of aqueous solution of Laponite under two conditions: (i) when the film is bounded by a wall, as in Petri dish experiments and (ii) when the film does not have any boundary, as in experiments with droplets. In order to obtain insights into the effect of the substrate, the experiments have been done with two different substrates of different hydrophobicities, polypropylene and glass. The formation of crack patterns has been explained on the basis of the wetting and spreading properties of the solution on these substrates and the effect of salt on colloidal aggregation. In this work, we have shown that the presence of salt in aqueous Laponite solution can induce crack patterns depending on the nature of the substrate. Another important aspect of this work is the role of NaCl in crack inhibition in desiccating films of aqueous Laponite, in the presence of static electric field. This effect can be utilized to suppress undesirable crack formation in many applications.

Electric convection of low-conductivity liquid in a horizontal capacitor in the presence of unipolar charge injection

Electric convection of low-conductivity liquid in a horizontal plane capacitor is analyzed with allowance for unipolar charge injection. Dynamics of charge transfer through stationary isothermal liquid in the presence of modulated electric field is studied. Effect of modulation amplitude and frequency on the spatiotemporal distribution of charge density and electric potential is considered. Nonlinear electric convection of nonisothermal low-conductivity liquid is studied in the presence of static electric field in a 2D system. Hysteresis transitions between two different (with respect to intensity) regimes of electric convection are analyzed.

Fast transport of water molecules across carbon nanotubes induced by static electric fields

Water permeation across a single-walled carbon nanotube has been studied in the presence of static electric fields (SEFs) with different directions under hydrostatic pressures. With the angle between the SEF direction and tube axis increasing from 0∘ to 90∘, the water flux decreases gradually until almost vanishes, and the maximum value at 0∘ is approximately four times the case without SEFs. The phenomenon is attributed to the alignment of the polar water molecules along the SEF direction. We also show that water permeation properties are dependent on the field strength due mainly to thermal fluctuations of water molecules.

Two-electron quantum ring in short pulses

The response of a two-electron quantum ring system to the short laser pulses of different shapes in the presence of external static electric field is studied. The variation of transition probabilities of the two-electron quantum ring from ground state to excited states with a number of parameters is shown and explained. The energy levels and wavefunctions of the system in the presence of static electric field are found by solving the time-independent Schrödinger equation numerically by the finite difference method. The shape of the pulse plays a dominant role on the dynamics.

Effects of transverse static electric field on terahertz radiation generation by beating of two transversely modulated Gaussian laser beams in a plasma

AbstractResonant excitation of terahertz (THz) radiation by nonlinear coupling of two filamented spatial-Gaussian laser beams of different frequencies and wave numbers is studied in plasma having transverse static electric field. The static ponderomotive force due to filamented lasers is balanced by the pressure gradient force which gives rise to transverse density ripple, while, the nonlinear ponderomotive force at frequency difference of beating lasers couples with density ripple giving rise to stronger transverse nonlinear current which results into the excitation of THz radiation at resonance. The coupling is further enhanced by the presence of static electric field and spatial-Gaussian nature of laser beams. An increase of six-fold in the normalized amplitude of THz is observed by applying a direct current field of about 50 KV. Effects of frequency, laser beam width, and periodicity factor of modulated laser amplitude are studied for the efficient THz radiation generation. These results can be utilized for generating controlled tunable THz sources for medical applications using low filament intensities (~ 1014 W/cm2) of beating lasers.

Crack Formation on a Drying Droplet in the Presence of Static Electric Field

The formation of crack patterns in a drying droplet of Laponite is studied under a DC (direct current) field. Though in the absence of a field, the droplet produces no crack on drying, it gives remarkable and reproducible results in the presence of a radial field. Cracks always appear from positive electrode and propagate towards the negative electrode and water seeps out from the negative electrode. When the centre electrode is negative, small cracks appear from outer periphery and the central portion remains almost free of crack. The behavior of cracks depends on the strength, direction and duration of application of field. The patterns show a typical memory effect different from 'Nakahara effect'. We name this as 'persistence memory'. From SEM (Scanning Electron Microscopy) images, it is seen that there are some striation marks left on the cracked surface, similar to cracks in larger systems.

Two-photon transitions in few-electron ions in the presence of static electric fields

Two-photon transitions in H- and He-like heavy ions in the presence of an external static electric field are explored using a relativistic Greens function approach and an independent particle model. The effects of Stark mixing on angular correlations, spectral distributions and total transition rates are analyzed in detail. Special emphasis is placed on the 2p1/2 → 1s1/2 two-photon transition in H-like ions and the 1s1/22p1/2:23P0 → 1s21/2:11S0 and 1s1/22s1/2:21S0 → 1s21/2:11S0 two-photon transitions in He-like ions.

Ultrafast coherent control of giant oscillating molecular dipoles in the presence of static electric fields

We propose a scheme to generate electric dipole moments in homonuclear molecular cations by creating, with an ultrashort pump pulse, a quantum superposition of vibrational states on electronic states strongly perturbed by very strong static electric fields. By field-induced molecular stabilization, the dipoles can reach values as large as 50 Debyes and oscillate on a time-scale comparable to that of the slow vibrational motion. We show that both the electric field and the pump pulse parameters can be used to control the amplitude and period of the oscillation, while preventing the molecule from ionizing or dissociating.

Crystallization of Poly(L -/D -Lactide) in the Presence of Electric Fields

We report, for the first time, an enhancement in melt crystallization kinetics of poly(L-/D-lactide) (a type-A1 polymer) in the presence of static electric fields as observed through measurement of the complex viscosity. Static electric fields of varying intensity (0–2.4 × 105 V m−1) are applied directly to the crystallizing polylactide melt at five different temperatures. The crystallization rate enhancement increases both with crystallization temperature and applied electric field intensity. An XRD analysis and optical microscopy studies allows us to attribute this to increased nucleation in the presence of an electric field. A technique allowing for the estimation of the rate of homogeneous nucleation induced by the electric field is developed.

Phase sensitive coherent control of atomic excitation in the presence of static electric fields: a frame transformation Stark theory approach

Phase sensitive coherent control on atomic Rydberg states and in the presence of a static electric field is theoretically studied using Harmin's frame transformation theory. It is shown that under the presence of the static field, the total excitation rate of an atomic target by a bichromatic laser field (consisting of a fundamental radiation frequency and of its second harmonic) depends on all the elements of the density-of-states matrix dictating the Stark effect. Some of these off-diagonal matrix elements are inaccessible by any other photoexcitation scheme and affect non-trivially the optimum achievable rate modulation contrast. This fact leads to important qualitative and quantitative differences with respect to static-field-free coherent control. The obtained formal expressions for the phase-controlled excitation rate are applied to the lithium target atom. It is demonstrated that the electric field strength can be used as an additional, externally adjustable, control and manipulation parameter. Finally, it is shown that above the saddle point energy, where quasi-discrete and continuum states coexist, the lineshapes of individual Fano-like resonances can be quite efficiently modified by applying this scheme.

One- and two-photon phase-sensitive coherent control of total ionization yields in the presence of static electric fields

We experimentally demonstrate one- and two-photon phase sensitive coherent control over the excitation and ionization of Rydberg states of Sr atom in the presence of a static homogeneous electric field. Without the field this excitation scheme can only be employed for the manipulation of angular distributions of photoelectrons and molecular photofragmentation products. Total atomic excitation-ionization yields cannot be modulated because the final states excited by each pathway are orthogonal to each other. When, however, a static electric field is applied, $s$, $p$ and $d$ character is admixed into the final Rydberg state, which has no definite parity anymore. Hence, the excitation of the target Stark state from the ground state is possible with either two (fundamental laser frequency) photons or one (second harmonic frequency) photon and its population and further ionization can be controlled by varying the relative phase between the two radiation fields. The concept is successfully tested below as well as above the classical saddle point and with either mutually crossed or parallel linear laser beam polarizations (while the second harmonic beam polarization vector is always parallel to the static field direction). We examine the behavior of the obtained photoionization signal modulation depth $V$ as a function of the static field strength $F$ for otherwise identical experimental conditions. The $V(F)$ curve exhibits a maximum (typically $\ensuremath{\sim}65%--85%$) at a field strength value that is dictated by the interplay between the employed laser power densities, one- and two-photon transition dipole moments, and relative amounts of field-dependent $s$, $p$ and $d$ character. It is therefore shown that the static field strength may serve as an additional, experimentally adjustable, control parameter in a fashion complementary to both the intensities and relative phase of the two light beams.

Polarization effects in high-harmonic generation in the presence of static-electric field

We study the ellipticity dependence of the high-order harmonic generation (HOHG) when a static electric field is presented. Through investigating the corresponding classical trajectories of the electron for the harmonic generation, it is found that there exists two different mechanisms. For circularly polarized incident light the HOHG originates mainly from the recombination of the electrons to the nucleus after multiple returns. We also find that for the elliptical incidence HOHG, the application of a static electric field can generate harmonics far beyond the usual cutoff.