Ionization Of Atomic Hydrogen Research Articles

Increase atom/molecular ratio of the hydrogen discharge

The high atomic to molecular ion ratio is important for hydrogen ion sources, but in the usual low-temperature hydrogen plasma the molecular ion component is dominating. Proton component can be increased by means of increasing plasma temperature, but in this case energy spectrum will be widened. Single electron collision with a hydrogen molecule may not only lead to the formation of the molecular ion, but also results in the formation of the proton. However, the cross section of the second process is much smaller than of the first (approximate ratio between them being 1:200). Thus, a single electron-molecule collision cannot be an efficient means of proton formation. Atomic hydrogen ions are produced by ionization of neutral hydrogen atoms. As a rule, a lifetime of neutral atoms is too short for ionization. The increase of the hydrogen atom lifetime by reducing the wall recombination coefficient allows us to get more protons. In this work we study the influence of water vapor injection on atom/molecular ratio of hydrogen plasma.

Photovoltage and photocurrent in Pd–oxide–InP structures in a hydrogen medium

Pd–oxide–InP (MOS) structures are fabricated, and their physical and photoelectric properties in a hydrogen atmosphere are investigated. It is established that a decrease in photovoltage of the structure and a large increase in photocurrent in the circuit are observed under the pulsed effect of hydrogen on the structure with a palladium layer illuminated by a light-emitting diode (LED of the wavelength λ = 0.9 μm). The kinetics and mechanism of the variation in the photovoltage and photocurrent are considered. It is assumed that the photovoltage decreases because of the ionization of hydrogen atoms in the Pd layer, and the photocurrent increases due to the thermionic emission of nonequilibrium electrons from the Pd layer into the semiconductor. On the basis of results of the investigations, the sensitive element for an optoelectronic hydrogen sensor is developed.

Coulomb effect on the left–right asymmetry in photoelectron emission with few-cycle laser pulses

We theoretically study the strong-field ionization of hydrogen atom in few-cycle laser pulses with the Coulomb–Volkov distorted-wave approximation (CVA) theory and focus on the role of the Coulomb potential in the left–right asymmetry of the photoelectron yields along the laser polarization direction, by comparing the CVA results with strong-field approximation (SFA) simulations. Our simulations show that the carrier-envelope phase (CEP) dependent asymmetry in CVA deviates from the SFA simulation and more interestingly, there is a phase shift of the asymmetry curve as a function of CEP when the laser intensity increases, contrary to what is expected in the SFA simulations. In terms of the simple man's model, the deviation of the asymmetry curves in CVA from the SFA simulations is attributed to the significant influence of the Coulomb potential on the forward rescattering electron which will get close to the core again after tunneling ionization. Furthermore, the laser-intensity dependence of the phase shift of the asymmetry curves in CVA is elucidated.

Relativistic Ionization of Hydrogen Atoms by Positron Impact

Relativistic triple differential cross-sections (TDCS) for ionization of hydrogen atoms by positron impact have been calculated in the symmetric coplanar geometry. We have used Dirac wave functions to describe free electron’s and positron’s sates. The relativistic formalism is examined by taking the non relativistic limit. Present results are compared with those for the corresponding electron-impact case. In the first Born approximation, we found that the TDCS for positron impact ionization exceeds that for electron impact for all energies in accordance with the result obtained by several other theories.

Loss of wave-packet coherence in ion-atom collisions

The projectile beam coherence effects occurring in ion-atom collisions are analyzed on the basis of the recent theory of Karlovets et al. [Phys. Rev. A 92, 052703 (2015)] developed for the elastic scattering of wave packets of particles off a potential field. This theory is generalized to estimate the loss of coherence for inelastically scattered projectiles in ionizing collisions. The results obtained by the suggested model are compared with experimental data for the ionization of hydrogen atoms and molecules by 75-keV proton impact. Significantly improved agreement is observed between the theory and experiment.

Photoelectron angular distributions in bichromatic atomic ionization induced by circularly polarized VUV femtosecond pulses

We investigate two-pathway interferences between nonresonant one-photon and resonant two-photon ionization of atomic hydrogen. In particular, we analyze in detail the photoionization mediated by the fundamental frequency and the second harmonic of a femtosecond VUV pulse when the fundamental is tuned near an intermediate atomic state. Following our recent study [Phys. Rev. A 91, 063418 (2015)PLRAAN1050-294710.1103/PhysRevA.91.063418] of such effects with linearly polarized light, we analyze a similar situation with circularly polarized radiation. As a consequence of the richer structure in circularly polarized light, characterized by its right-handed or left-handed helicity, we present and discuss various important features associated with the photoelectron angular distribution.

An Angular Distribution of Three Photon Ionization in Presence of Multiple Laser Beams

<p>We have studied the effect of phase difference between different multiple beams on the photoelectron angular distribution in three photon ionization of atomic hydrogen by using Dalgarno-Lewis methods. It has been found that both total and photo-electron angular distribution vary with laser intensity, phase and polarization of different beams. Intensity dependance of corresponding assymetry parameters has also been studied. We have shown that this variation with laser intensity is caused by two effects: the effect of phase and polarization of different beams. Asymmerties of azimuthal angular distribution are emphasized.</p><p>Journal of Nepal Physical Society Vol.3(1) 2015: 18-22</p>

The First Born Triple Differential Cross-Section for Ionization of H(3P) by Electron Impact in the Asymmetric Coplanar Geometry

First Born triple differential cross sections (TDCS) for ionization of metastable 3P-state hydrogen atoms by electrons are calculated for various kinematic conditions in the asymmetric coplanar geometry. A multiple scattering theory is used in this study. The present results are compared with other existing related theoretical results for ionizations of hydrogen atoms from metastable 2S-state and 2P-state, showing a good qualitative agreement. There is no available theoretical study for ionization of metastable 3P-state hydrogen atoms by electrons. We are expecting that the present results provide a wide scope for further study of such ionization problems.

Differential ionization of a one-electron target under bare-ion impact: Application to proton-impact ionization of atomic hydrogen

Differential ionization of a one-electron target under bare-ion impact: Application to proton-impact ionization of atomic hydrogen

Extension of the wave packet molecular dynamics method towards the accurate quantum simulations of electron dynamics

In this paper, we review a multiple-wavepacket version of the Antisymmetrized Wave Packet Molecular Dynamics (AWPMD), that may be utilized to increase the accuracy and the performance of this quantum simulation method. The original WPMD method is based on parameterization of the electron wave function by a single Gaussian wave packet. It gives qualitatively better results than the classical Molecular Dynamics but the quantitative description of essentially quantum systems is rather poor. In this work, we describe a new technique based on multiple Gaussian expansion of the single-electron wave function, which is called Split Wave Packet Molecular Dynamics (SWPMD). The related theoretical formalism is given, followed by the analysis of static and dynamical properties of a quantum system of several particles, where the simulation results may be compared to the theoretical predictions. The tests are based on ionization of hydrogen atom under a strong laser pulse. We demonstrate that the SWPMD method may significantly improve the accuracy of the model wave function and enables one to simulate the quantum branching processes, including the tunneling, which was impossible in the single-wavepacket version of the method.

A study of the turn-up effect in the electron momentum spectroscopy

Recently, a number of electron momentum spectroscopy measurements for the ionization of atoms and molecules have shown that the triple differential cross section (TDCS) has an unexpected higher intensity in a low momentum regime (Brunger M J, Braidwood S W, Mc Carthy I E and Weigold E 1994 J. Phys. B: At. Mol. Opt. Phys. 27 L597, Hollebone B P, Neville J J, Zheng Y, Brion C E, Wang Y and Davidson E R 1995 Chem. Phys. 196 13, Brion C E, Zheng Y, Rolke J, Neville J J, McCarthy I E and Wang J 1998 J. Phys. B: At. Mol. Opt. Phys. 31 L223, Ren X G, Ning C G, Deng J K, Zhang S F, Su G L, Huang F and Li G Q 2005 Phys. Rev. Lett. 94 163201, Deng J K, et al 2001 J. Chem. Phys. 114 882, Ning C G, Ren X G, Deng J K, Su G L, Zhang S F and Li G Q 2006 Phys. Rev. A 73 022704). This surprising result is now called the turn-up effect. Our aim is to investigate such an effect by studying the case of the ionization of atomic hydrogen in an excited state using the 3C model (Brauner M, Briggs J S and Klar H 1989 J. Phys. B: At. Mol. Opt. Phys. 22 2265) which is able to describe all the measured results of the single ionization of atomic hydrogen in its ground state for an incident energy beyond 200 eV. A comparison is also made of the findings of the present method with those of the plane wave impulse approximation and distorted wave models.

A variationally stable method in the problem of two-photon atomic ionization

A variationally stable method is analyzed; it is one of the rarely used approaches for calculating the amplitudes of nonlinear photoprocesses in the framework of perturbation theory. The convergence of the method is studied based on the example of atomic hydrogen and hydrogenlike ions. The method is used to calculate the angular distributions of photoelectrons for the first time.

Relativistic calculation of the electron momentum shift in tunneling ionization

SynopsisWe describe a procedure for the solution of the time-dependent Dirac equation. The procedure is based on the relativistic generalization of the matrix iteration method. We use this procedure to study electron momentum distribution along the laser beam propagation direction for the process of the tunneling ionization of hydrogen atom. We found, in agreement with the experimental observations [1], that relativistic effects lead to appreciable deviation of the distribution from the strict left-right symmetry present in the non-relativistic case. The expectation value of the momentum along the laser beam propagation direction grows linearly with intensity and follows closely the behavior of the expectation value of the kinetic energy divided by the speed of light. These features agree with the experimental results [1].

Variational study of atomic hydrogen ionization by electrons impact

SynopsisTriple differential cross section results of the electron impact ionization of hydrogen atom are performed in the so-called Schwinger-Born approximation of variational principle of Schwinger. In the theoretical calculations the first Born term was calculated analytically, and the second Born term was determined in the closure approximation using semi-analytical calculations. The theoretical results were corrected by the so-called Gamow factor in order to include post-collision effects, then compared with experiments performed with an incident electron energy of Ei = 250 eV and with those of other models. Better agreement was found between our results and experimental data even for high values of the ejected electrons energy (50 eV).

Non-constant ponderomotive energy in above threshold ionization by intense few-cycle laser pulses

SynopsisWe analyze the above threshold ionization of hydrogen atom by strong and short laser pulse with a simple envelope temporal dependence. We find additional peaks in the resulting ATI spectra originated from different values of the ponderomotive energy and the interference due to the electronic emission at different times.

A study of the turn-up effect in the Electron Momentum Spectroscopy

SynopsisWe show that the PWIA model completely fails for any ionization of atomic hydrogen in its initial state or in an excited state. The results of our study are compared with those of the 3C or BBK model.

Photoexcitation and ionization of hydrogen atom confined in Debye environment

The dynamics of a hydrogen atom confined in an impenetrable spherical box and under the effect of Debye screening, in the presence of intense short laser pulses of few femtosecond (fs) is studied in detail. The energy spectra and wave functions have been calculated using Bernstein polynomial (B-polynomial) method. Variation of transition probabilities for various transitions due to changes in Debye screening length, confinement radius as well as the parameters characterizing applied laser pulse is studied and explained.

On the Theory of Hydrogen Atom Ionization by Ultra‐Short Electromagnetic Pulses

AbstractAn investigation of the probability of hydrogen atom ionization by ultra‐short electromagnetic pulses is carried out in the frame of perturbation theory We consider the case when the electric field strength amplitude E0 in a pulse by two orders lower than characteristic atomic field strength Ea (Ea ≅ 5.1 · 109 V/cm). A detailed investigation of the dependence of the probabilities on the pulse duration was performed for Gaussian pulse shapes. In the case where the carrier frequency of the Gaussian pulse is larger than the atomic ionization potential, the probability goes to the standard limit of perturbation per unit time. At the same pulse durations, the probabilities for carrier frequencies less than the ionization potential go to zero. The frequency dependence of the ionization probability becomes equal to the standard threshold dependence with increasing pulse duration time. A comparison between the ionization effects caused by wavelet pulses without carrier frequency and Gaussian pulses with carrier frequency shows that the same ionization probability values are achieved when the pulse carrier frequency is detuned by about 20% from the ionization threshold. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Pulse-shape effects in ionization of atomic hydrogen by short-pulse XUV intense laser radiation: A sensitivity study

The displacement effect studied in a recent paper [Ivanov et al., Phys. Rev. A 90, 043401 (2014)] in atomic ionization by a short XUV pulse is investigated in more detail. It is shown that achieving a significant displacement critically depends on the assumption of a plateau in the envelope function of the electric field, and that the ramp-on is fine-tuned in such a way that a drift velocity generated during the ramp-on phase can increase this displacement further. Seemingly minor variations in the electric fields defined in slightly different ways cause significant changes in the final results, in particular regarding the angular-momentum distribution of the ejected electron. In light of such a strong sensitivity seen in the predictions made with idealized pulse shapes and the likely difficulties of preparing such pulses experimentally, an experimental realization of the displacement effect will likely be a major challenge.

Influence of dense quantum plasmas on fine-structure splitting of Lyman doublets of hydrogenic systems

Relativistic calculations are performed to study the effects of oscillatory quantum plasma screening on the fine-structure splitting between the components of Lyman-α and β line doublets of atomic hydrogen and hydrgen-like argon ion within dense quantum plasmas, where the effective two-body (electron–nucleus) interaction is modeled by the Shukla–Eliasson oscillatory exponential cosine screened-Coulomb potential. The numerical solutions of the radial Dirac equation for the quantum plasma-embedded atomic systems reveal that the oscillatory quantum screening effect suppresses the doublet (energy) splitting substantially and the suppression becomes more prominent at large quantum wave number kq. In the absence of the oscillatory cosine screening term, much larger amount of suppression is noticed at larger values of kq, and the corresponding results represent the screening effect of an exponential screened-Coulomb two-body interaction. The Z4 scaling of the Lyman doublet splitting in low-Z hydrogen isoelectron...