Range Of Field Intensities Research Articles

Atom under an intense laser pulse: Stabilization effect and strong-field approximation

Direct numerical calculations of the single-photon ionization dynamics of the hydrogen atom were compared with the data obtained within the strong-field approximation (SFA). An analysis showed that the SFA model accurately determines the range of electromagnetic field intensities, upon reaching of which the ionization mode deviates from that described within perturbation theory; in particular, the ionization rate decreases with increasing intensity. It was demonstrated that the actual ionization mechanism under an intense pulse differs significantly from the SFA predictions. For example, an analysis of photoelectron angular distributions and energy spectra showed that the strong-field ionization features within the SFA model are primarily controlled by the ionization channel closing effect associated with the ponderomotive shift of the continuum boundary. At the same time, the results of direct numerical calculations of the ionization dynamics suggest that the Kramers-Henneberger atom is formed in a strong field, which is characterized by increased stability to strong-field ionization.

Equilibrium shapes of a ferrofluid drop

AbstractA numerical solution strategy for calculating equilibrium free surfaces of a ferrofluid drop under the action of uniform magnetic fields is proposed. Based on this strategy, drop shapes of nonlinear magnetisable fluids are obtained numerically in a wide range of field intensities and compared with existing theoretical results. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanomagnetic Behavior of Fullerene Thin Films in Earth Magnetic Field in Dark and Under Polarization Light Influences

In this paper magnetic fields intensity of C60 thin films of 60 nm and 100 nm thickness under the influence of polarization lights are presented. Two proton magnetometers were used for measurements. Significant change of magnetic field intensity in range from 2.5 nT to 12.3 nT is identified as a difference of dark and polarization lights of 60 nm and 100 nm thin films thickness, respectively. Specific power density of polarization light was 40 mW/cm2. Based on 200 measurement data average value of difference between magnetic intensity of C60 thin films, with 60 nm and 100 nm thickness, after influence of polarization light, were 3.9 nT and 9.9 nT respectively.

In vivo NMR imaging evaluation of efficiency and toxicity of gene electrotransfer in rat muscle

In vivo gene electrotransfer (ET) is a simple method of gene delivery in various tissues relying on the injection of plasmid DNA followed by application of electric pulses. Noninvasive tools are needed to evaluate the ET efficiency and the resulting tissue damages. In this study, we performed ET of rat tibialis muscle after injection of either a plasmid coding for luciferase or a contrast agent (CA) detected by using magnetic resonance imaging (MRI). Plasmid expression and CA intracellular trapped quantity were compared throughout the electric field intensity range 0-300 V/cm. Although the CA trapped quantity reflects only the electropermeabilization step, both measurements were correlated. MRI measurements gave easy access to tridimensional visualization of the labelled zones where the CA has been injected and the applied electric field had a value allowing permeabilization. We also performed MRI measurements of the water transverse relaxation time T2 as an indicator of tissue modification, and tested whether another CA specific for necrosis could be used to detect muscle necrosis at high electric field intensity. In conclusion, MRI measurements may bring multiparametric information upon the efficiency and tissue toxicity of an ET protocol by using a simple and safe CA.

Behavior of molecular hydrogen exposed to strong dc, ac, or low-frequency laser fields. II. Comparison ofab initioand Ammosov-Delone-Krainov rates

Ionization rates are calculated for molecular hydrogen oriented parallel to an external electric or low-frequency electromagnetic field using a three-dimensional, fully correlated ab initio method. The calculation includes also the range of field intensities where barrier suppression leads to over the barrier instead of tunneling ionization. The resulting ionization rates (considering also the influence of vibrational motion and excitation) are compared to those predicted by the (semiclassical) Ammosov-Delone-Krainov (ADK) model. In agreement with earlier findings for helium it is found that the ADK model predicts very accurately ionization rates in the tunneling regime, but overestimates the rate in the over-the-barrier regime. This conclusion is, however, only true, if the tunnel-ionization rate of ${\mathrm{H}}_{2}$ is (at least to a good approximation) isotropic.

Multiphoton above-threshold detachment ofLi−:Exterior-complex-scaling– generalized-pseudospectral method for calculations of complex-quasienergy resonances in Floquet formulation of time-dependent density-functional theory

We extend the exterior-complex-scaling--generalized-pseudospectral (ECSGPS) method [D. A. Telnov and S. I. Chu, Phys. Rev. A 59, 2864 (1999)] to the nonperturbative calculations of complex-quasienergy resonances of many-electron quantum systems within the Floquet formulation of time-dependent density-functional theory (TDDFT) [D. A. Telnov and S. I. Chu, Chem. Phys. Lett. 264, 466 (1997)]. The ECSGPS technique appears very useful in TDDFT-Floquet calculations where the exchange-correlation potentials may exhibit quite complicated behavior as functions of the electron coordinates and cannot be easily treated by means of the uniform-complex-scaling techniques. We have applied this procedure to the study of one-photon detachment and two-photon dominant above-threshold detachment of ${\mathrm{Li}}^{\ensuremath{-}}$ negative ions. In the one-photon case, the photodetachment cross section has been calculated as a function of the photon energy with results in good agreement with the experimental data. In the two-photon case, both the partial detachment rates and electron angular distributions for the dominant and above-threshold channels are presented for a range of laser field frequencies and intensities. Dramatic transformations of the angular distributions in the vicinity of the two-photon threshold are observed and analyzed.

A novel cavitation probe design and some preliminary measurements of its application to megasonic cleaning

Cavitation is an effective physical mechanism for concentrating mechanical energy. Accordingly, it has wide applications in such diverse fields as sonochemistry, in which chemical reactions are initiated or accelerated, or in the electronic component cleaning industry in which particles (and other materials) are removed from surfaces. However, devices designed to act as cavitation monitors have had little success, partly because their intrusiveness often affects the cavitation field itself. Presented here is a brief description of a unique cavitation monitor that utilizes the phenomenon of sonoluminescence as an indirect quantifier of cavitation. It appears to work efficiently over a broad range of acoustic field intensities and its application to megasonic cleaning has provided interesting and valuable insights into this technology.

Influence of External Electric Fields on Reaction Fronts in the Iodate−Arsenous Acid System

The propagation of arsenous acid−iodate reaction fronts of different net stoichiometries in externally applied dc electric fields is studied for a range of both electric field intensities and initial compositions of the reacting mixture (represented by the stoichiometric factor S0). Regions of three different types of net stoichiometry in the parametric space ℰ/V vs S0, where ℰ is the intensity of the applied electric field and V the reaction front propagation velocity, are determined both experimentally and by analyzing a reaction−diffusion−migration model that includes a realistic kinetic scheme of the reaction studied. Both agreement with and discrepancies between the theoretical predictions and experimental findings are discussed.

Amplification of a probe field without population inversion in a two-level atom driven by a strong bichromatic pump field

The polarization spectrum of a two-level atom driven by a symmetrical bichromatic pump field is examined. It is shown that the heterodyne parametric four-wave interactions result in the amplification of a weak probe field without population inversion at the line center in a wide range of pump and probe field intensities.

The Evolution of Pores and the Development of Penumbrae

We investigate the evolution of the magnetic field in an emerging active region near disk center using data from the Advanced Stokes Polarimeter. Specifically, we follow the formation of a pore from a radiatively undisturbed region and the formation of a protospot, i.e., the appearance of a rudimentary penumbral sector for a mature pore. Our approach is to use the temporal evolution of bivariate distribution functions correlating continuum intensity, Ic, magnetic field magnitude, | ${b B}$ --> |, magnetic fill fraction, f, local inclination, ?, local azimuth, , and line-of-sight Doppler velocity, vD. The highlights of our results include, (1) in the pore-forming region, a preference for the relatively strong vertical field points (1000-1500 G) to be redshifted (downflowing) and the appearance of dark pore points to be at the expense of radiatively undisturbed points; (2) an onset flux of ? 2 ? 1019 Mx in a dark pore that appears in an area in which the flux increases by ? 1 ? 1020 Mx prior to the pore's appearance and that previously contained an azimuth center, i.e., a magnetic concentration that otherwise has no continuum-intensity signature; (3) a threshold of (1-1.5) ? 1020 Mx above which a partial penumbra forms; (4) the appearance of penumbral elements that at once having the appropriate penumbral range of field strengths, intensities, and inclination angles, i.e., no obvious gradual increase in the magnetic fields' inclination with increasing flux during the formation of penumbrae; (5) no delay between the appearance of inclined penumbral magnetic fields and the Evershed flow; and (6) a self-similarity between the pore, protospot, and a small mature sunspot with respect to the (| ${b B}$ --> |, Ic), (| ${b B}$ --> |, ?), (f, ?), and the (vD, Ic), (vD, ?) distributions.

Dielectric properties and structure of pure and doped (Mn, Fe, Co, Cu) PLZT 8/65/35

Abstract The PLZT 8/65/35 compund, commonly known for relaxor behaviour, as well as PLZT 8/65/35+Me compositions (Me ‒ 3d elemment: Mn, Fe, Co, Cu) is examined a number of different technuques being used: 1) dielectric measurements of complex permeability ϵ* (v, T, E) at frequencies from 10−1 to 107 Hz in the range of temperature from 0 to 200°C; 2) Raman scattering (RS), EPR, X-ray diffraction (XRD) at 20°C. Behaviour of ϵ (v, T, E) is interpreted assuming existence of three differenct polarization mechanisms the partial contributions to the dielectric constant of which depends on dopant concentration and the range of frequency, temperature or field intensity. Structural criteria are proposed to evaluate contributions of each of the mechanisms.

An efficient method for determining quantum dynamics in strong fields by integrating through amplitude and frequency parameter space

A new method which computes the dynamics of molecular systems under the influence of a strong field is presented. Eigenvalues and eigenfunctions of the time-dependent Schrödinger equation are obtained and integrated over a range of field amplitudes and frequencies, and the evolution of the wavefunction is determined using Floquet formalism. With this method, it is possible to predict the wavefunction dynamics for an arbitrary range of field intensities and wavelengths by solving the time-dependent Schrödinger equation only once or, in some cases, by not solving it at all, even though the field intensities are well within the nonperturbative regime. Large savings in computational time are demonstrated in application of the method to vibrational excitation of hydrogen fluoride.

Loss from magneto-optical traps in strong laser fields.

We present results for the behavior of loss rates in magneto-optical traps in strong fields. They show that the trap loss rate does not saturate along with the excitation process. On the contrary, it increases with the laser-field intensity inside the region of saturation of the laser transition. We also show that an alternative method, the adiabatic formulation of the optical Bloch equations, can be used to predict the behavior of trap loss over a wide range of temperatures and field intensities.

Strong-field high-frequency approximation to the multiphoton ionization of hydrogen

The strong-field multiphoton ionization of atoms is considered and a theoretical approach dealing nonperturbatively with the radiation field formulated. The general computational scheme is the conventional perturbation theory, but the intermediate states are dressed by the field. We present in detail a method to dress the continuum states and to study the dipole transitions within the continuum. In the high-frequency domain, the proposed procedure rapidly converges over a wide range of field intensity and offers an interesting framework for calculating ionization rates for arbitrary numbers of absorbed (above-threshold) photons and field polarization.

Anomalous increase of the density scale length in a double-frequency laser plasma.

The analytic expressions for steady-state electric field intensity and local density scale length in a plasma irradiated by a double-frequency laser are derived. It is shown that the ponderomotive force due to the double-frequency laser field leads to a local density dip near the critical surface and to the anomalous increase and fluctuation of the critical density scale length in some range of field intensity.

Multiphoton ionization and collisions in strong laser fields

Two elementary atomic processes are investigated: multiphoton ionization of the hydrogen atom and multiphoton free–free transitions under the influence of high-intensity laser radiation. The first process is investigated using the S-matrix formalism allowing for the Coulomb field of ions and for the field of laser radiation acting on the final states of the ejected electrons. It is shown that a simple model allowing for field fluctuations makes the results qualitatively very close to the actual experimental observations. The second process is discussed by generalization of the well-known results on the balance between absorption and emission in a wide range of field intensities and for different numbers of exchanged photons.

Development of a laced electromagnetic wiggler

The construction of a one-period wiggler system called a laced wiggler is presented along with test results from a prototype design. The laced electromagnetic wiggler is being developed to attain higher magnetic fields, shorter wavelengths, and larger gaps for the induction-linear accelerator, free-electron-laser (FEL) program. In the laced wiggler design, permanent magnets are located (laced) between the electromagnetic coils to increase the reverse-bias flux in the iron pole beyond that possible with only pole-edge (side) permanent magnets. This increase in reverse-bias flux allows wiggler operation at midplane magnetic-field intensities comparable to those of a hybrid permanent magnet/steel wiggler, but with field adjustability over a specified range. The maximum field intensity and tuning range are selected, within limits, for specific design requirements. The test results show good agreement with the analytical predictions and confirm the ability of the laced wiggler to attain the desired midplane magnetic flux density and tuning range. Both the nominal wiggle field along the wiggler axis and the focusing field variation are within the acceptable limits of design requirements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of microwave characteristics of photoconductive IC structures

A one-dimensional analytic solution for the microwave photoresponse of an optically modulated semiconductor channel is presented. This extends the existing treatments by including the effects of nonuniform channel cross sections and conductivity, nonuniform optical illumination, field-dependent mobilities, nonzero dielectric relaxation times, arbitrary electrical and optical excitation frequencies, and full coupled bipolar carrier transport. The solution is continuous over the full range of electric field intensities and thereby describes both the saturated and nonsaturated regimes of the photocurrent. Only the low-level generation case is considered, and trapping effects and diffusion are not included. This model allows the effects of optical stimulation in many typical IC structures to be assessed from dc up through the microwave range of frequencies.

A new variational approach to the hydrogen atom in magnetic fields

We develop a simple and useful variational method to obtain approximate eigenenergies and expectation values ofr2 andρ2 for a hydrogenlike atom in a magnetic field. Results agree quite well with accurate numerically computed ones in the whole range of field intensities.

The effect of electrostatic field direction on the diffusion of charged dust particles from the flowstream to a sphere

The diffusion of charged aerosol particles from the flow to an isolated spherical collector under the influence of an electrostatic field is studied numerically. The dust concentration in the diffusional layer surrounding the sphere is calculated for an electric field aligned with the flow direction, opposite to it and transverse to the flow. The dimensionless mass transfer coefficient is evaluated for a wide range of electrostatic field intensities. The Sherwood numbers for the various electrostatic field orientations are compared with available analytical solutions.