Shift Of He Research Articles

Reexamining the Stark width and shift of He ii Paschen-α: Studies using laser-induced plasma, Thomson scattering, and computer simulations.

We report on experimental and theoretical studies on the Stark profile of the Heii Paschen-α line over a wide range of plasma parameters. This line was emitted from a laser-induced plasma with electron densities in the range of 8.1×10^{22}-4.46×10^{24}m^{-3} and electron temperatures of 1.2-7.6eV as independently measured using the two-color Thomson scattering method. The line shapes were calculated using a computer simulation method, treating the ions and electrons on an equal footing and taking into account the full Coulomb interaction between the hydrogenlike atomic radiator and plasma perturbers penetrating the wave-function extent of the bound electron. We found a very good agreement between the experimental and theoretical Stark widths and shifts, which on average agree within 5%. In addition, practical analytical approximations for the linewidth and line shift are provided, validated against extensive calculations in the density and temperature ranges of 10^{23}-10^{25}m^{-3} and 1-16eV, respectively.

Helium Metastable Distributions and Their Effect on the Uniformity of Hydrogenated Amorphous Silicon Depositions in He/SiH4 Capacitively Coupled Plasmas

This study investigates, numerically, the spatial distribution of metastable helium (He*) in He/SiH4 capacitively coupled plasma (CCP) for the purpose of optimizing plasma density distributions. As a first step, we presented the results of a two-dimensional fluid model of He discharges, followed by those of He/SiH4 discharges to deposit hydrogenated amorphous silicon films, to investigate which factor dominates the coating uniformity. We retained our CCPs in the 300 mm wafer reactor used by the semiconductor industry in the recent past. Selected parameters, such as a sidewall gap (radial distance between the electrode edge and the sidewall), electrical condition of the sidewall, and position of the powered electrode, were considered. In addition, by increasing the gas pressure while varying the sidewall condition, we observed modification of the plasma distributions and, thus, the deposition rate profiles. According to the results, the shift in He* distributions was mainly due to the reduction in the electron mean free path under conditions of gas pressure higher than 100 Pa, as well as local perturbations in the ambipolar electric field due to the finite electrode structure. Small additions of SiH4 largely changed the He* density profile in the midplane of the discharge due to He* quenching. Furthermore, we found that the wide sidewall gap did not improve deposition uniformity against the expectation. This was because the excitation and ionization rate profiles were enhanced and localized only near the bottom electrode edge.

Revisiting the Stark Width and Shift of He II Pα

We report experimental determination of plasma-induced Stark widths and shifts of the He II P α line and a comparison of the results with calculations performed by several computational approaches. The measurements were carried out in a small compressing plasma channel device, reaching electron densities in excess of 10 18 cm − 3 and temperatures of a few eV. The experimental data are in a good agreement with some previously published studies. However, the measured relation between the Stark shift and width could not be reproduced by either of the codes, and this disagreement is not yet resolved. This suggests the existence of an additional effect that is not accounted for in the present models and leads to a larger than expected Stark shift of the He II P α line.

Infrared diode laser spectroscopy of the Kr–N2O van der Waals complex: the v 1 symmetric stretch region of N2O

The rovibrational spectra of four isotopomers of the Kr–N2O van der Waals complex, namely 82Kr–N2O, 83Kr–N2O, 84Kr–N2O and 86Kr–N2O, were measured in the v 1 vibrational band region of the N2O monomer (∼1285 cm−1) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. Rotational constants for both ground and excited vibrational states of these four isotopomers were accurately determined. The band-origin of Kr–N2O was observed to shift by +0.1065 cm−1 from that of the monomer. The band-origin shifts of Rg–N2O (Rg = Ne, Ar, Kr) in the v 1 vibrational band region could also be well explained by the model based on a Buckingham intermolecular potential [W.A. Herrebout, H.-B. Qian, H. Yamaguchi and B.J. Howard, J. Mol. Spectrosc. 189, 235 (1998)]. But the band-origin shift of He–N2O was found to deviate significantly from this model. The possible reason is discussed and the band-origin shift of Xe–N2O predicted.

Illuminating the proton radius conundrum: the μHe+ Lamb shiftThis paper was presented at the International Conference on Precision Physics of Simple Atomic Systems, held at École de Physique, les Houches, France, 30 May – 4 June, 2010.

We plan to measure several 2S–2P transition frequencies in μ4He+ and μ3He+ by means of laser spectroscopy with an accuracy of 50 ppm. This will lead to a determination of the corresponding nuclear rms charge radii with a relative accuracy of 3 × 10−4, limited by the uncertainty of the nuclear polarization contribution. First, these measurements will help to solve the proton radius puzzle. Second, these very precise nuclear radii are benchmarks for ab initio few-nucleon theories and potentials. Finally when combined with an ongoing measurement of the 1S–2S transition in He+, these measurements will lead to an enhanced bound-state QED test of the 1S Lamb shift in He+.

Lamb shift inHe+: Resolution of a discrepancy between theory and experiment

Lamb shift in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mo>:</mml:mo></mml:math> Resolution of a discrepancy between theory and experiment

Maximal acceleration corrections to the Lamb shift of hydrogen, deuterium and He +

The maximal acceleration corrections to the Lamb shift of one-electron atoms are calculated in a nonrelativistic approximation. They are compatible with experimental results, are in particularly good agreement with the 2 S2 P Lamb shift in hydrogen and reduce by ∼ 50% the experiment-theory discrepancy for the 2 S2 P shift in He +.

Shift of the He II Pαline in high density plasmas

The authors have measured the shift of the line He II 468.57 nm at electron densities ranging from 1 to 6*1023m-3at 4 eV. A value of 0.0155 nm at 1023m-3was measured. A linear variation with the density is observed. Three different effects supposed to be responsible for the shift are reviewed. Comparison of the authors' results with theory is precluded by the large uncertainty concerning the plasma polarisation shift. Good agreement is observed with previous measurements.

Non-doppler shift of He II slow modes in a pressure released partially packed superleak

Abstract Pressure released bulk superfluid waves are not Doppler shifted by a persistent current in a superleak partially filling the channel.

A comparison of self broadening and shift of helium, neon and argon emission lines

Self broadening (van der Waals and resonance) and shift of Ne emission lines and van der Waals broadening and shift of He emission lines have been measured using a high pressure (0.5–3.0 atom), low current discharge. These results are compared with previous measurements in Ar and He to obtain a complete comparison of self broadening and shift of He, Ne and Ar emission lines. Oscillator strengths for the resonance transitions are obtained from the resonance broadening coefficients. The trend of the van der Waals broadening coefficients for the three noble gases is correctly predicted by a theory due to HINDMARSH et al. (4) in which a Lennard-Jones potential is used in the impact theory formalism. The measured line shifts cannot be accounted for by this theory and reflect the need for more accurate quantum mechanical calculations.

Pressure broadening and shift of the first diffuse series doublet of indium due to the presence of helium and argon

The shift and half-width of In λ 3039 and In λ3256 was measured in Ar and He under pressures up to one thousand p.s.i. The temperature of the absorption tube was 850°C for In λ 3039 and 930°C for In λ 3256. The van der Waals interaction constant for In/Ar was found to be 1·5 x 10 -30 and 8·6 x 10 -31 cm 6/sec for In λ 3039/Ar and In λ 3256/Ar respectively. In λ 3256 exhibited a small red shift in He for the range of r.d. (from 1 to 16) of He employed.