Ionization Of Atomic Hydrogen Research Articles

Numerical investigation on circular interference photoelectron momentum distributions induced by spatiotemporal optical vortex pulse

Using the strong field approximation theory, we conducted a detailed numerical investigation on the photoelectron momentum distributions (PMDs) arising from the ionization of hydrogen atoms by a circularly polarized spatiotemporal optical vortex (STOV) pulse. STOV pulses have a unique spatial structure and peculiar phase properties. Our simulations reveal that PMDs exhibit a complex interference structure characterized by circular momentum bands intertwined with intricate interference fringes. A thorough examination of the multi-photon process provides a comprehensive explanation for the circular momentum band formation. We develop an expression to elucidate their center momentum positions within the PMDs. Furthermore, we perform a detailed analysis of the fine interference fringes, attributing their origin to the singular phase of the STOV pulse. Despite their distinct manifestations, we infer that the circular momentum bands and fine interference fringes stem from the simultaneous dependence upon the space and time variables of the STOV phase.

Low-energy atomic and molecular hydrogen ion interaction with low-work function electride 12CaO · 7Al2O3

To efficiently generate H− ions from positive atomic or molecular hydrogen beams injected onto a solid surface, it has been suggested to use a material with a low-work function as the target material. However, it is not clear under what conditions the most efficient H− production is realized for incident beam parameters or reflection angles. Therefore, we studied the interaction between low-energy atomic and molecular hydrogen beams (less than 1 keV/nucleon) with a low-work function electride 12CaO⋅7Al2O3 (C12A7). The production ratio of H− to H+ ions from the C12A7 electride was much higher than Mo targets with higher work functions, especially at smaller incident and smaller reflection angles. The H− to H+ production ratio slightly increased as the incident energies were decreased, but there was no significant difference between the electride and Mo targets. These results indicate that smaller incident angles and lower beam energies of the incident hydrogen beam are favorable for the enhancement of the production ratio of H− to H+ ions in C12A7. The higher production ratio appeared at the vertical beam energies less than on the order of 100 eV, where quantum mechanical processes may become important.

Ionization of hydrogen atom driven by ultrashort intense laser pulses: study in momentum space of phase-dependent effects

Ionization of hydrogen atom driven by ultrashort intense laser pulses: study in momentum space of phase-dependent effects

Electron vortex generations in photoionization of hydrogen atoms by circularly-polarized chirped attosecond pulses

By numerically solving the time-dependent Schrödinger equation and employing the analytical perturbative model, we investigated the chirp-induced electron vortex in the photoionization of hydrogen atoms by a pair of counter-rotating circularly polarized chirped attosecond extremely ultraviolet pulses. We demonstrated that single-photon ionization of hydrogen atoms generates photoelectron momentum distributions (PMDs) with distinct helical vortex structures either with or without a time delay between two counter-rotating circularly polarized laser pulses. These structures are highly sensitive to both the time delay between the pulses and their chirp parameters. Our analytical model reveals that the splitting of vortex spirals is caused by the sign changing of the chirp-induced frequency-dependent time delay. We showed that to obtain the counterpart of the PMD under a pair of counter-rotating circularly polarized chirped pulses, both chirp parameters and ordering of pulses need to be reversed.

Strong‐Field Ionization of Hydrogen Atom Driven by Quantum Light (Invited)

Strong‐Field Ionization of Hydrogen Atom Driven by Quantum Light (Invited)

Multiphoton excitation and ionization of hydrogen atoms in two-color laser fields

Multiphoton excitation and ionization of hydrogen atoms in two-color laser fields

Ionization of Hydrogen Atom by Proton Impact—How Accurate Is the Ionization Cross Section?

For the control of fusion reactors, we need to accurately know all the possible reactions and collisional cross sections. Although large-scale trials have been performed over the last decades to obtain this data, many basic atomic and molecular cross section data are missing and the accuracy of the available cross sections need to be checked. Using the available measured cross sections and theoretical predictions of hydrogen atom ionization by proton impact, critical analysis of the data is presented. Moreover, we also present our recent classical results based on the standard classical trajectory Monte Carlo (CTMC) and quasi-classical trajectory Monte Carlo (C-QCTMC) models. According to our model calculations and comparison with the experimental data, recom-mended cross sections for ionization of hydrogen were presented in a wide range of pro-jectile impact energies. We found that, while in the low energy region, the experimental cross sections are very close to the C-QCTMC results, at higher energies, they are close to the results of our standard CTMC results.

Strong-Field Ionization of Hydrogen Atoms with Quantum Light.

We study the strong-field ionization driven by quantum lights. Developing a quantum-optical-corrected strong-field approximation model, we simulate the photoelectron momentum distribution with squeezed-state light, which manifests as notably different interference structures from that with coherent-state (classical) light. With the saddle-point method, we analyze the electron dynamics and reveal that the photon statistics of squeezed-state light fields endows the tunneling electron wave packets with a time-varying phase uncertainty and modulates the photoelectron intracycle and intercycle interferences. Moreover, it is found the fluctuation of quantum light imprints significant influence on the propagation of tunneling electron wave packets, in which the ionization probability of electrons is considerably modified in time domain.

Numerical investigation on Coulomb impact on bouquetlike photoelectron momentum distributions

Deploying the strong-field approximation and the saddle point methods, we numerically simulate the Coulomb impact on the bouquetlike photoelectron momentum distributions (PMDs) induced by intense laser ionization of hydrogen atom. The bouquet-like PMDs, also dubbed as electron carpet-like PMDs, are interference structures perpendicular to laser polarization in PMDs. The results show that the bouquetlike interference PMDs are mostly altered for small momenta, for both the above-threshold ionization (ATI) and intra-cycle interference (ICI) fringes, compared with the Coulomb-free situation. We propose a correlation parameter (CP) to quantitatively elucidate the PMDs alterations due to Coulomb effect. Also, we formulate an expression for successfully tracing out the ATI and ICI fringes, which proves that the bouquetlike PMDs alterations are attributed to an extra action phase due to Coulomb interaction.

Controlling Magnetic and Electric Nondipole Effects with Synthesized Two Perpendicularly Propagating Laser Fields

Nondipole effects are ubiquitous and crucial in light-matter interaction. However, they are too weak to be directly observed. In strong-field physics, motion of electrons is mainly confined in transverse plane of light fields, which suppresses the significance of nondipole effects. Here, we present a theoretical study on enhancing and controlling the nondipole effect by using the synthesized two perpendicularly propagating laser fields. We calculate the three-dimensional photoelectron momentum distributions of strong-field tunneling ionization of hydrogen atoms using the classical trajectory Monte Carlo model and show that the nondipole effects are noticeably enhanced in such laser fields due to their remarkable influences on the sub-cycle photoelectron dynamics. In particular, we reveal that the magnitudes of the magnetic and electric components of nondipole effects can be separately controlled by modulating the ellipticity and amplitude of driving laser fields. This novel scenario holds promising applications for future studies with ultrafast structured light fields.

Antiproton impact ionization of hydrogen atom: Differential cross sections computed by Coulomb wave function discrete variable representation method

Our aim is using the Coulomb wave function discrete variable representation method (CWDVR) for the calculation of collision problem in first time. Nonrelativistic collision of antiproton with hydrogen atom is described by solving the time-dependent Schrodinger equation numerically. Two collision amplitudes are used for calculation of the differential cross sections, one of them corresponds to impact parameter of the projectile while other one is determined by projectile momentum transfer and found by Fourier transform of the first one. The ionization amplitude calculated by projecting of the wave function onto continuum wave function of the ejected electron. The differential cross sections calculated depending on projectile impact energy, scattering angle and electron ejection energy and angles, which is a result that can be measured experimentally. Our results are in good agreement with the relativistic calculation results.

Effects of Hydrogen on Endurance Characteristics in NAND Flash Memories

This study comprehensively investigates the effect of hydrogen content in forming gas annealing (FGA) on the endurance of NAND flash memories by statistically analyzing the transconductance () characteristics. The degradation () worsened with higher cycling temperature, delayed time period from erasing to programming () operation, and higher word-line bias () during Moreover, these effects become more pronounced as the hydrogen content in FGA increases. Using the measured distributions and Monte -Carlo TCAD technology, the activation energy () of oxide damage creation can be extracted. The extracted values were 50 meV and 160 meV for the diluted (4%) and pure (100%) hydrogen samples, respectively. This suggests that a higher hydrogen concentration results in more ionized hydrogen atoms remaining in the oxide layer. During these hydrogen ions can drift near the Si/SiO2 surface, where they may react to form trap states. is revealed to have a linear relationship with respect to where the slope is independent of the hydrogen content in FGA.

Photoelectron momentum distributions in the strong-field ionization of atomic hydrogen by few-cycle elliptically polarized optical pulses

We investigate the strong-field ionization of atomic hydrogen in a few-cycle elliptically polarized infrared pulse by solving the time-dependent Schr\"odinger equation. The dependence of the photoelectron momentum distribution on the pulse intensity, ellipticity, length, envelope, and carrier envelope phase is analyzed. In particular, we explain the variation of the electron offset angle with asymptotic electron energy through the combined action of the field and the Coulomb potential, and demonstrate that low-ellipticity pulses make it possible to access the electron release time.

Roles of the transition amplitude phases in photoelectron asymmetry of single strong attosecond pulse

The angular distributions of the photoelectrons in ionization of hydrogen atom by both circularly and linearly polarized intense extreme ultraviolet (XUV) attosecond pulse are investigated by numerically solving the time-dependent Schrödinger equation. We clearly identify nonperturbative features in studying the asymmetrical photoelectron angular distributions in the polarization plane for the XUV photon energy (16.3 eV) close to the ionization threshold, while such nonperturbative features are absent for higher photon energy (36 eV) in the same pulse intensity region. In addition to the carrier-envelope phase (CEP) dependence, the ejection asymmetry of the photoelectron is also sensitive to the relative phases of transition amplitudes in absorbing one photon and two photons. As a consequence, the CEPs corresponding to the maximal (or zero) asymmetry obviously vary as the pulse intensity increases in a moderately large region from 1 × 1015 W cm−2 to 30 × 1015 W cm−2. We attribute the intensity dependence of the transition amplitude phases to a consequence of the depletion of population as well as the Stark energy shift of the initial state. We show that the relative phases of transition amplitudes can be precisely decoded from the pulse intensity dependence of the ejection asymmetry and those phases are insensitive to the ellipticity of the laser pulse.

Duoplasmatron type molecular carbon ion source

An ion source capable of producing molecular ions delivers a beam of impurity dopant for shallow ion implantation of semiconductor device fabrication. Production and transport of low energy molecular ions is indispensable for tabulating fundamental data on plasma-wall interactions that should be used to design a future nuclear fusion reactor. An ion source plasma can produce molecular ions of solid materials by sputtering, while low temperature plasma efficiently transports produced molecular ions to the source extraction hole. A duoplasmatron ion source with the carbon plasma electrode has successfully produced poly-atomic carbon ions up to C6 +. The intermediate electrode has six holes to guide cathode plasma to the carbon anode performing as the plasma electrode. A 1 mm diameter extraction hole is opened at the center of the carbon plasma electrode, where is no direct exposure to the plasma from the cathode region. The ion source maintains a stable discharge with both H2 and Ar as discharge support gas, but works better at lower pressure with Ar. A hydrogen plasma produced molecular ions of hydrocarbons with the mass separated current of C3H5 + with the intensity comparable to other ion species including atomic, diatomic and triatomic hydrogen ions.

Nonadiabatic Strong Field Ionization of Atomic Hydrogen.

We present experimental data on the nonadiabatic strong field ionization of atomic hydrogen using elliptically polarized femtosecond laser pulses at a central wavelength of 390nm. Our measured results are in very good agreement with a numerical solution of the time-dependent Schrödinger equation (TDSE). Experiment and TDSE show four above-threshold ionization peaks in the electron's energy spectrum. The most probable emission angle (also known as "attoclock offset angle" or "streaking angle") is found to increase with energy, a trend that is opposite to standard predictions based on Coulomb interaction with the ion. We show that this increase of deflection angle can be explained by a model that includes nonadiabatic corrections of the initial momentum distribution at the tunnel exit and nonadiabatic corrections of the tunnel exit position itself.

Energetic pickup proton population downstream of the termination shock as revealed by IBEX-Hi data

ABSTRACT Pickup protons originate as a result of the ionization of hydrogen atoms in the supersonic solar wind, forming the suprathermal component of protons in the heliosphere. While they are being picked by the heliospheric magnetic field and convected into the heliosheath, the pickup protons may suffer stochastic acceleration from the solar wind turbulence in the region from the Sun up to the heliospheric termination shock, where they can also experience shock-drift acceleration or reflection from the cross-shock potential. These processes create a high-energy tail in the pickup ion energy distribution. The properties of this energetic pickup proton population are still not well defined, in spite of the fact that they are vital for models that simulate energetic neutral atom fluxes. We consider two scenarios for the pickup proton velocity distribution downstream of the heliospheric termination shock (a filled shell with an energetic power-law tail, and bi-Maxwellian). Based on a numerical kinetic model and observations of the energetic neutral atom fluxes from the inner heliosheath by the IBEX-Hi instrument, we characterize the pickup proton distribution and provide estimations of the properties of the energetic pickup proton population downstream of the termination shock.

Electron spectra for twisted electron collisions

Ionization collisions have important consequences in many physical phenomena, and the mechanism that leads to ionization is not universal. Double differential cross sections (DDCSs) are often used to identify ionization mechanisms because they exhibit features that distinguish close collisions from grazing collisions. In the angular DDCS, a sharp peak indicates ionization through a close binary collision, while a broad angular distribution points to a grazing collision. In the DDCS energy spectrum, electrons ejected through a binary encounter collision result in a peak at an energy predicted from momentum conservation. These insights into ionization processes are well-established for plane wave projectiles. However, the recent development of sculpted particle wave packets reopens the question of how ionization occurs for these new particle wave forms. We present theoretical DDCSs for (e, 2e) ionization of atomic hydrogen for electron vortex projectiles. Our results predict that the ionization mechanism for vortex projectiles is similar to that of non-vortex projectiles, but that the projectile’s momentum uncertainty causes noticeable changes to the shape and magnitude of the vortex DDCSs. Specifically, there is a broadening and splitting of the angular DDCS peak for vortex projectiles, and an increase in the cross section for high energy ejected electrons.

Jet propagation through inhomogeneous media and shock ionization

AbstractIn this contribution, we present the first numerical simulations of a relativistic outflow propagating through the inner hundreds of parsecs of its host galaxy, including atomic and ionized hydrogen, and the cooling effects of ionization. Our results are preliminary, but we observe efficient shock ionization of atomic hydrogen in interstellar clouds. The mean density of the interstellar medium in these initial simulations is lower than that expected in typical galaxies, which makes cooling times longer and thus no recombination is observed inside the shocked region. The velocities achieved by the shocked gas in the simulations are in agreement with observational results, although with a wide spectrum of values.

Electric resistivity of partially ionized plasma in the lower solar atmosphere

The lower solar atmosphere is a gravitationally stratified layer of partially ionized plasma. We calculate the electric resistivity in the solar photosphere and chromosphere, which is the key parameter that controls the rate of magnetic reconnection in a Sweet-Parker current sheet. The calculation takes into account the collisions between ions and hydrogen atoms as well as the electron-ion collisions and the electron-hydrogen atom collisions. We find that under the typical conditions of the quiet Sun, electric resistivity is determined mostly by the electron-hydrogen atom collisions in the photosphere, and mostly by the ion-hydrogen collisions, i.e. ambipolar diffusion, in the chromosphere. In magnetic reconnection events with strong magnetic fields, the ambipolar diffusion, however, may be insignificant because the heating by the reconnection itself may lead to the full ionization of hydrogen atoms. We conclude that ambipolar diffusion may be the most important source of electric resistivity responsible for the magnetic flux cancelation and energy release in chromospheric current sheets that can keep a significant fraction of neutral hydrogen atoms.