Measurements of electron density and Stark width of neutral helium lines in a helium arc plasma

Electron densities in an atmospheric helium arc plasma have been measured with the Stark broadening parameters of helium spectral lines. The spatially distributed radiation intensities are converted to plasma emission coefficients at every wavelength by means of Abel inversion. From the inverted profiles of He I lines of 4713 ?, 5016 ?, and 6678 ? electron density has been calculated, which ranges from 0.5 ×10¹⁶ to 4 ×10¹⁶ cm^-3 for a helium arc with current 200 A. Stark widths of He I lines of 3889 ? and 7065 ? are determined based on the measurements and compared with existing data.     

Investigations on ionic processes and dynamics in the sheath region of helium and hydrogen discharges by laser spectroscopic electric field measurements

Temporally and spatially resolved measurements of the electric field distribution in the sheath region of RF and dc discharges provide a detailed insight into the sheath and ion dynamics. The electric field is directly related to the sheath ion and electron densities, the sheath voltage, and the displacement current density. Under certain assumptions also the electron and ion conduction current densities at the electrode, the ion current density into the sheath from the plasma bulk, the ion energy distribution function, and the power dissipated in the discharge can be inferred. Furthermore, the electric field distribution can give an indication of the collision-induced conversion between different ion species in the sheath. Laser spectroscopic techniques allow the noninvasive in situ measurement of the electric field with high spatial and temporal resolution. These techniques are based on the spectroscopic measurement of the Stark splitting of Rydberg states of helium and hydrogen atoms. Two alternative techniques are applied to RF discharges at 13.56 MHz in helium and hydrogen and a pulsed dc discharge in hydrogen. The measured electric field profiles are analyzed, and the results discussed with respect to the ion densities, currents, energies, temporal dynamics and species composition. Received: 26 July 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001     

Superradiant transitions between high-lying levels of Sr in an external electric field

Superradiant transitions were observed between high lying levels in Sr. The transitions react very sensitively to an external electric field. Superradiant cascades or one transition in a superradiant branching can be suppressed. The square root of the high of a superradiant pulse decreases with the second power of the electric field strength. This behaviour can be explained by calculations.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

Motional Stark Effect and Its Active Cancellation in Diamagnetic Spectrum of Barium

With time-of-flight and electric field ionization detection technique, we investigate the motional Stark effect for highly excited Rydberg barium in high magnetic field and its active cancellation experimentally. In the experiment, the atom beam is aligned at a small angle of 15° with respect to the magnetic field. The motional Stark effect cancellation is demonstrated on two sets of. circularly polarized spectra in static magnetic field B = 1.00000 Tesla and B = 1.70000 Tesla, respectively, although the effect is very small （- 3.5 Vcm^-1） in our apparatus configuration.     

On the use of relative line intensities of forbidden and allowed components of several HeI lines for electric field measurements

In this Letter we propose a method for electric field measurements based on intensity ratio of forbidden and allowed helium lines. HeI 402.6 nm, HeI 447.1 nm, and HeI 492.1 lines and their forbidden components are used for the measurement of electric field strength in the cathode region of the abnormal glow discharge in helium-hydrogen mixture. Electric filed strength was independently determined using polarization spectroscopy of Hβ line and then compared with electric filed strength obtained from relative intensity of HeI forbidden and allowed lines.     

Photodetachment of H- in a static electric field

We derive a formula using closed-orbit theory for the photodetachment cross-section of H^- in the presence of a static electric field when there is an arbitrary angle θ_L between the laser polarization direction and the static electric field. This formula generalizes the previous result for laser polarization parallel to the static electric field, the effect of laser polarization direction appears as a factor cos²(θ_L) in the amplitude of the oscillation. A photodetachment cross-section formula valid above and below detachment threshold is proposed.     

On the Stark broadening of Sr+ and Ba+ resonance lines in ultracold neutral plasmas

We report results of the Stark broadening calculations for Sr⁺ and Ba⁺ resonance lines in ultracold plasmas using semiempirical formulas and numerical computer simulation technique. The simulation results show that strong collisions dominate Stark broadening at very low electron temperatures and weak collision approximation used recently by Vrinceanu et al. cannot be applied in this temperature region. Consequently, the temperature trend of Stark widths and shifts changes from successfully used at elevated temperatures to an increasing trend with temperature, which is characteristic for strong collisions at low temperature.     

Effects of an electric field on the confined hydrogen atom in a parabolic potential well

Using the perturbation method, the confined hydrogen atom by a parabolic potential well is investigated. The binding energy of the confined hydrogen atom in a parabolic potential well is calculated as a function of the confined potential radius and as a function of the intensity of an applied electric field. It is shown that the binding energy of the confined hydrogen atom is highly dependent on the confined potential radius and the intensity of an applied electric field.     

Classical study of the rovibrational dynamics of a polar diatomic molecule in static electric fields

We study the classical dynamics of a polar diatomic molecule in the presence of a strong static homogeneous electric field. Our full rovibrational investigation includes the interaction with the field due to the permanent electric dipole moment and the polarizability of the molecule. Using the LiCs molecule as a prototype, we explore the stability of the equilibrium points and their bifurcations as the field strength is increased. The phase space structure and its dependence on the energy and field strength are analyzed in detail. We demonstrate that depending on the field strength and on the energy, the phase space is characterized either by regular features or by small stochastic layers of chaotic motion.     

Scaling properties of composite information measures and shape complexity for hydrogenic atoms in parallel magnetic and electric fields

The scaling properties of various composite information-theoretic measures (Shannon and Rényi entropy sums, Fisher and Onicescu information products, Tsallis entropy ratio, Fisher-Shannon product and shape complexity) are studied in position and momentum spaces for the non-relativistic hydrogenic atoms in the presence of parallel magnetic and electric fields. Such measures are found to be invariant at the fixed values of the scaling parameters given by and . Numerical results which support the validity of the scaling properties are shown by choosing the representative example of the position space shape complexity. Physical significance of the resulting scaling behavior is discussed.     

Stark shifts and fine structure of the Li 3 D states

⁶Li 3²D _{3/2, 5/2} states were studied using a diode laser to first excite the 2P _3/2 state and a dye laser to populate the 3²D _{3/2, 5/2} states. The dye laser was modulated by an electro-optic modulator and intersected an atomic beam that passed through a field free region and subsequently through a uniform electric field. A value of 1084.24±0.20 MHz was found for the 3²D fine structure splitting. The scalar and tensor polarizabilities were determined to be α (3D _3/2 ) = - 3.753±0.015, α ₂ (3D _3/2 ) = 2.893±0.017, α (3D _5/2 ) = - 3.772±0.008 and α ₂ (3D _5/2 ) = 4.058±0.013 MHz/(kV/cm)². Received 26 September 2002 / Received in final form 22 January 2003 Published online 11 March 2003 RID="a" ID="a"e-mail: wlaser@yorku.ca     

Spectroscopic observation of the plasma produced by a CO2 laser beam interacting with titanium target under helium and/or argon atmosphere

In many laser applications such as drilling, welding and cutting, the role of the plasma in the transfer of energy between the laser beam and the metal surface appears to be rather important. It depends on several parameters such as laser wavelength, irradiation time and deposited energy but especially on the buffer gas nature. In this work the plasma is initiated by a TEA-CO₂ laser beam perpendicularly focussed onto a Ti target (100 MW/cm²), in a cell containing He, Ar or a He-Ar mixture as buffer gas. The plasma is studied by time and space resolved spectroscopic diagnostics. The results show that helium allows target erosion whereas a highly absorbing breakdown plasma develops in argon shielding the target from the subsequent laser heating. With only 20% Ar in He, a strong quenching of the He plasma by Ar occurs, and the Ar plasma effect is dominant.     

Bright optical lattices in a longitudinal magnetic field. Experimental study of the oscillating and jumping regimes

All the bright optical lattices studied so far have been designed to obtain a circularly polarized light at the bottom of the optical potential wells. This condition minimizes the departure rate of the atoms from the fundamental adiabatic surface and permits an oscillating regime in a large range of parameters. We present here an experimental study of cesium atoms in a three-dimensional optical lattice, where the light is linearly polarized at the bottom of the potential wells. Temperature measurements and pump-probe spectroscopy give similar results for this lattice and for the conventional lin lin lattice (which have circular polarizations at the bottom of the wells) despite the fact that one lattice operates in the jumping regime and the other in the oscillating regime. We study the behaviour of the two types of lattices in a longitudinal magnetic field, with particular emphasis on the zero field and strong field regimes. The strong field situation is very simple because the eigenstates are then almost pure Zeeman substates and the adiabatic and diabatic potential surfaces are identical. The comparison between the zero-field and the high-field situations shows that the diabatic potentials are more appropriate to account for experimental observations in the novel lattice. Received: 9 October 1997 / Accepted: 6 November 1997     

Photoionization of atoms in parallel electric and magnetic fields: Cross-section calculations using the Lanczos algorithm and the complex coordinate method in a discrete variable representation

A combination of the complex-coordinate method and the Lanczos recursion scheme is implemented in the discrete variable representation (DVR) to obtain total photoionization cross-sections using an iterative procedure. Applications to photoionization of hydrogen atoms in electric fields and sodium atoms in electric and parallel electric and magnetic fields are presented and discussed. Received 15 May 2000 and Received in final form 4 October 2000     

Measurement of the optical Stark effect in semiconducting carbon nanotubes

A strong optical Stark effect has been observed in (6,5) semiconducting single-walled carbon nanotubes by femtosecond pump-probe spectroscopy. The response is characterized by an instantaneous blueshift of the excitonic resonance upon application of pump radiation at photon energy well below the band gap. The large Stark effect is attributed to the enhanced Coulomb interactions present in these one-dimensional materials.     

Measurement of the gas temperature in a glow discharge by fluorescence spectroscopy

From the measurement of the distribution of sputtered iron atoms over the fine structure levels of the iron groundstate (a ⁵ D), the gas temperature of an argon glow discharge (p=1 Torr) has been derived under collision dominated conditions at distances larger than 30 mean free paths from the iron cathode.     

Characterization of different magnetite–cobalt nanoparticles in hydrocarbon-based magnetic fluids by means of static and dynamic magnetization measurements

Magnetic nanoparticles with different compositions (Co_xFe_3−xO₄, 0?x?0.1) were synthesized from metal salts using a coprecipitation technique to produce magnetic fluids following a peptization technique. The liquid carrier was the hydrocarbon Isopar M and the surfactant was oleic acid. The colloidal-sized ferrimagnetic nanoparticles produced were found to be superparamagnetic. Measurements of the complex magnetic susceptibility were carried out to evaluate the resonant frequency f_res, the anisotropy constant K, and anisotropy field H_A. f_res was found to be a linear function of the cobalt content of the magnetic nanoparticles over the range of cobalt content studied.     

Oscillator strengths of the 4s4p~^{{\mathsf{1,3}}}P1↦ 4snd~^{\mathsf {1,3}}D2 transitions of neutral calcium

A detailed study has been performed for estimating the orbital energies, positions and shifts of the Lyman lines of C⁵⁺, Al¹²⁺ and Ar¹⁷⁺ under strongly coupled plasma with a view to understand such line positions and shifts obtained in laser produced plasma experiments. The effect of strongly coupled plasma has been treated within the Ion Sphere (IS) model. Both non-relativistic and relativistic methods have been used for estimating the spectral properties. Theoretical estimates with IS model of the plasma are in conformity with the results of laser plasma experiments on these highly stripped ions. The experimental data for the systems have also been compared with the theoretical estimates using Debye screening model of the plasma with spatial confinements which gives additional restrictions to the wave functions at finite boundaries.