Recoil Momentum Research Articles

Mode-channel interdependence of the vibrational excitations associated withK-shell photoionization of CO2

It is shown that the direction of the photoelectron recoil momentum transferred to the photoion influences molecular photoionization dynamics, resulting in the appearance of a specific mode--channel interdependence. We disclose the interdependence and the interplay of the core-hole- and photoelectron-induced recoil effects by passing to normal mass-dependent modes in both coordinate and momentum spaces. As an example, the vibrational structure of the $1{s}^{\ensuremath{-}1}$ photoelectron line of $\text{C}{\text{O}}_{2}$ is investigated in detail. The intensity of bending and symmetric and asymmetric stretching vibrational and rotational excitations is found to differ substantially in the $\ensuremath{\Sigma}\ensuremath{\rightarrow}\ensuremath{\Sigma}$ and $\ensuremath{\Sigma}\ensuremath{\rightarrow}\ensuremath{\Pi}$ photoionization channels.

Theory and molecular dynamics simulations of intrinsic localized modes and defect formation in solids

Molecular dynamics (MD) simulations of recoil processes following the scattering of x-rays or neutrons have been performed in ionic crystals and metals. At small energies (< 10 eV) the recoil can induce intrinsic localized modes (ILMs) and linear local modes associated with these modes. As a rule, the frequencies of such modes are located in the gaps of the phonon spectrum. However, in metallic Ni, Nb and Fe, due to the renormalization of atomic interactions by free electrons, the frequencies mentioned are found to be positioned above the phonon spectrum. It has been shown that these ILMs are highly mobile and can efficiently transfer a concentrated vibrational energy over large distances along crystallographic directions. If the recoil energy exceeds tens of eVs, vacancies and interstitials can be formed, which are strongly dependent on the direction of the recoil momentum. In NaCl-type lattices the recoil in (110) direction can produce a vacancy and a crowdion, while in the case of a recoil in (100) and in (111) directions a bi-vacancy and a crowdion can be formed.

Carrier-envelope-phase dependence of asymmetric C[sbnd]D bond breaking in C2D2 in an intense few-cycle laser field

The carrier envelope phase (CEP) dependence in the CD bond breaking of C2D2 induced by an intense few-cycle laser pulse is investigated. The ejection direction of D+ ions generated from the Coulomb explosion, C2D22+→C2D+ and D+, exhibits the CEP dependent asymmetry, while its CEP dependence is out of phase by π with respect to the CEP dependence of the recoil momentum of C2D2+. From a recollisional double ionization model, the asymmetry in the ejection direction of D+ was ascribed to the laser-assisted CD bond weakening in the few-cycle laser field.

Physics of Small Recoil Momenta in One Photon-Two-Electron Ionization of Helium

Physics of Small Recoil Momenta in One Photon-Two-Electron Ionization of Helium

О верификации методов определения импульса отдачи в микро-наноньютоновом диапазоне при лазерной абляции твердотельных мишеней

О верификации методов определения импульса отдачи в микро-наноньютоновом диапазоне при лазерной абляции твердотельных мишеней

Experimental investigation of recoil-momentum-generation efficiency under near-IR femtosecond laser ablation of refractory metals in vacuum

The use of ultrashort laser pulses is a way to increase recoil momentum under laser ablation of materials, because, in this case, the energy deposition per unit volume of the target material is substantially higher due to reduced heat dissipation. By using methods of combined interferometry, we estimated the specific impulse (∼200–900 s), momentum coupling coefficient (∼2 × 10−5−3 × 10−4 Ns/J), laser-energy conversion efficiency to kinetic energy of the gas-plasma flow (∼0.05–0.82), and degree of the gas-plasma flow monochromaticity (∼0.72–0.92) under femtosecond (τ ∼ 45 fs, λ ∼ 800 nm) ablation of refractory metals (Ti, Zr, Mo, and Nb) in vacuum.

SEMILEPTONIC DECAY OF Bc MESON INTO $c\bar c$ STATES IN A QCD POTENTIAL MODEL

The slope and curvature of Isgur–Wise function for Bc meson is computed in a QCD potential model in two different approaches of choosing the perturbative term of the Cornell potential. Based on heavy quark effective theory the exclusive semileptonic decay rates of Bc meson into the [Formula: see text] states are exploited. Spin symmetry breaking effects are ignored up to a particular point and the form factors are connected with Isgur–Wise function for other kinematic point since the recoil momentum of [Formula: see text] from Bc is small due to its heavy mass.

Observation of spatter formation mechanisms in high-power fiber laser welding of thick plate

This paper aims to present the dynamic behaviors of spatter formation, and to clarify the spatter formation mechanisms in the high-power fiber laser welding of a thick plate at low welding speeds. We used a modified “sandwich” specimen to directly observe the geometry of the longitudinal keyhole wall. The dynamic behaviors of the keyhole, vapor plume, and melt pool with the formation of spatters were observed using high-speed imaging. The mechanisms of the formation of the spatter ejected from the top and bottom surfaces were analyzed. The recoil momentum associated with the energized vapor plume jet acts on the tips of the gauffers on the front keyhole wall and micro-droplets inside the keyhole, thereby resulting in the formation of high-speed micro-spatter. At partial penetration, the spatter ejected from the keyhole inlet is influenced mainly by the upward melt flow above the keyhole, melt displacement around the keyhole, and the strong shear stream of the directed vapor plume force. Moreover, some spatter droplets are accelerated through the vapor plume outside the keyhole. At full penetration of the melt, spatters are generated when the downward momentum of the melt due to downward flow and gravity, or vapor burst with an open keyhole, exceeds the surface tension forces. At full penetration of the keyhole, the crucial driving force for spatter generation is the viscous friction drag associated with high-speed motion of the energized vapor plume through the open keyhole. The welding process evolves into almost a cutting process at a lower welding speed.

Efficiency of recoil momentum generation during femtosecond laser ablation of copper in vacuum

thrusters. Introduction. Increasing the effi ciency of recoil momentum generation during laser ablation of condensed media is crucial for the development of laser induced controlled thermonuclear fusion (1) and the development of laser-plasma thrusters (2). It is also important for the creation of gas-plasma fl ow injectors (3), technologies for direct laser-induced transport of matter (4), laser-plasma deposition of thin fi lm coatings (5), and the initiation of processes in micro-electromechanical systems (6). When laser radiation with an energy density (fl uence) exceeding the ablation threshold is incident on condensed materials, a gas-plasma fl ow is generated which is characterized by the number and velocity distribution of the particles drawn into the fl ow. When a metal is irradiated, the laser energy is absorbed in a thin (~10 -8 -10 -7 m) layer at the surface, so that the volume density of absorbed laser energy is high. The high thermal conductivity of metals means that this energy spreads into the depth of the material, with the size of the thermal interaction zone being proportional to the duration of the laser pulse (7). The velocity of the atoms and ions in the laser induced gas-plasma fl ow depends substantially on the fraction of the absorbed energy that is dissipated as heat (8).

Cross section calculations of photoabsorption and Compton scattering contributions to He single and double ionization via recoil momentum observable

This paper presents a theoretical framework for the calculations of Compton scattering and photoabsorption on bound electrons for single and double ionization, based on recoil-ion observable. For the photoionization of helium (single or double) our calculations of cross sections for photon energy of 7keV show that the recoil ions from photoabsorption are mainly distributed on a sphere in momentum space of 22a.u. radius, while recoil ions from Compton scattering show a dominant contribution close to zero radius (≲3a.u.). Our calculated cross sections are in agreement with the published experimental values.

Numerical Simulation on Laser Propulsion Capability of Polymer Target

A computational model of laser ablated polymer was established. Set the ablation criterion based on threshold energy. Put forward the polymer ablation criterion in the numerical model. It established the energy distribution equation to describe the laser ablation process. When the ablation products ejected, the target gained recoil impulse from ejection process. Get the ejection energy and the recoil momentum of target based on momentum conservation law. The numerical analysis model can reflect the propulsion capability of different polymer propellant, revealed the law of propulsion parameters in laser ablation process.

Small molecule photoelectron spectroscopy: Recoil effects, stoichiometric surprises, and double-core-hole ionization

Three features of small-molecule photoelectron spectroscopy are considered (1) the atom from which a photoelectron is emitted must have a recoil momentum equal to that of the emitted electron. This is shared among the various modes of motion of the ion, leading to rotational and vibrational excitation. Furthermore, any initial velocity of the atom (due to either translational, rotational, or vibrational motion) will lead to Doppler broadening. These effects are observable and can, in general, be accounted for by simple models. In some cases, however, the simple models fail and a deeper insight is necessary. (2) Inner-shell photoionization is essentially an atomic process, and it is expected that the intensity for emission of a photoelectron from the core of an atom in a molecule will be independent of its chemical environment. Recent measurements on the carbon 1s photoelectron spectra of three chloroethanes show that this is not the case. At energies not far above the ionization threshold there are strong oscillations of the intensity ratio (CCl/CH) with increasing photon energy. These are similar to those seen in EXAFS and can be accounted for by considering backscattering of the photoelectrons from the chlorine atoms. Moreover, even at high energies the cross section for ionization has been found to depend on the chemical environment of the atom. These results have important consequences for the use of inner-shell electron spectroscopy for quantitative analysis. (3) Single-core-hole ionization energies have long been used as a tool for investigating chemical phenomena. Double-core-hole ionization energies provide additional chemical information. By combining the single-hole and double-hole ionization energies it is possible to determine the effects of the initial-state charge distribution and final-state charge rearrangement on the chemical shifts and on other chemical properties. Until recently double-core-hole ionization energies have not been experimentally accessible for first-row elements. New experimental techniques have, however, made it possible to measure these not only for single sites in a molecule, but also for two different sites in the same molecule. The chemical information that can be obtained from such measurements is discussed.

Development of 4π detector to clarify fragmentation dynamics of molecule in collisions with highly charged ions in ultra low energy region

We have developed a new detector to study collision dynamics between highly charged ion and molecule in ultra low energy region (≤ 1 keV/u). The outline of this detector is a recoil momentum spectroscopy in semi-spherical energy analyzer. At the conference, we will present progress report of the developments of this detector including TOF spectra of recoil ions in coincidence with HCI after collisions.

Triple differential cross section calculations for the ionization of molecular nitrogen by electron impact

TDCSs for the ionization of N2 by electron impact were calculated. The kinematical conditions of the ionization process imply intermediate impact energies and large ion recoil momentum.

Positron-impact ionization studied by means of Recoil-Ion momentum distributions

We investigate ionization processes induced by positron impact by studying the momentum distributions of the receding ion by means of Classical Trajectory Monte Carlo techniques. We compare the recoil momentum distributions with those of the electron and positron.

H + D2 Reaction Dynamics in the Limit of Low Product Recoil Energy.

Both experiment and theory recently showed that the H + D2(v = 0, j = 0) → HD(v' = 4, j') + D reactions at a collision energy of 1.97 eV display a seemingly anomalous HD product angular distribution that moves in the backward direction as the value of j' increases and the corresponding energy available for product recoil decreases. This behavior was attributed to the presence of a centrifugal barrier along the reaction path. Here, we show, using fully quantum mechanical calculations, that for low recoil energies, the collision mechanism is nearly independent of the HD internal state and the HD product becomes aligned, with its rotational angular momentum j' pointing perpendicular to the recoil momentum k'. As the kinetic energy to overcome this barrier becomes limited, the three atoms adopt a nearly collinear configuration in the transition-state region to permit reaction, which strongly polarizes the resulting HD product. These results are expected to be general for any chemical reaction in the low recoil energy limit.

Matter–antimatter gigaelectron volt gamma ray laser rocket propulsion

It is shown that the idea of a photon rocket through the complete annihilation of matter with antimatter, first proposed by Sänger, is not a utopian scheme as it is widely believed. Its feasibility appears to be possible by the radiative collapse of a relativistic high current pinch discharge in a hydrogen–antihydrogen ambiplasma down to a radius determined by Heisenberg's uncertainty principle. Through this collapse to ultrahigh densities the proton–antiproton pairs in the center of the pinch can become the upper gigaelectron volt laser level for the transition into a coherent gamma ray beam by proton–antiproton annihilation, with the magnetic field of the collapsed pinch discharge absorbing the recoil momentum of the beam and transmitting it by the Moessbauer effect to the spacecraft. The gamma ray laser beam is launched as a photon avalanche from one end of the pinch discharge channel. Because of the enormous technical problems to produce and store large amounts of anti-matter, such a propulsion concept may find its first realization in small unmanned space probes to explore nearby solar systems. The laboratory demonstration of a gigaelectron volt gamma ray laser by comparison requiring small amounts of anti-matter may be much closer.

(e,2e)processes on atomic targets (Ne, Ar) and molecular targets (CH4, N2, CO2): Role of electron-nucleus scattering

The momentum distributions of the recoil ions were measured for the single ionization of atomic targets (Ne, Ar) and of molecular targets (CH${}_{4}$, N${}_{2}$, CO${}_{2}$) at incident electron energies ranging from 80 to 220 eV by using the reaction microscope. It was found that there are a remarkable number of recoil ions with large longitudinal momenta, and the relative contribution of these ions for Ne ($e$, 2$e$) reactions decreases faster than that for Ar ($e$, 2$e$) reactions with the incident electron energy increasing. This observed feature can be qualitatively interpreted by the different effective potential of the target core experienced by the electrons. The appearance of the large longitudinal momentum recoil ions for CH${}_{4}$, N${}_{2}$, and CO${}_{2}$ ($e$, 2$e$) reactions indicates that the strong interaction between the electron and the component-atoms target core in the molecules plays a significant role in the single ionization of small molecular targets. Depending on the independent atom model, we can intuitively understand the characteristics of the momentum distributions of the recoil ions CH${}_{4}^{+}$, N${}_{2}^{+}$, and CO${}_{2}^{+}$, respectively.

Testing the equivalence between the canonical and Minkowski momentum of light with ultracold atoms

We design an experimental system to test the equivalence between the canonical and Minkowski momentum of light, which can provide a judgment on the recent resolution of the century-old Abraham-Minkowski controversy by S. M. Barnett [Phys. Rev. Lett. 104, 070401 (2010)]. By measuring the recoil momentum of ultracold rubidium atoms in a rubidium Bose-Einstein condensate after the electromagnetically induced absorption of a monochromatic laser pulse, the momentum of the pulse in the ultracold atoms can be obtained. If the equivalence is valid, the measured results will coincide with the theoretical values of the canonical momentum of the pulse. Otherwise, if the equivalence is invalid, the measured results will coincide with the theoretical values of the Minkowski momentum, which are significantly different from that of the canonical momentum. Our scheme is amethod to test the equivalence between the canonical and Minkowski momentum of light. It can also be improved to distinguish between the Minkowski and Abraham momenta to contribute to the study of the Abraham-Minkowski controversy in the future.

State-selective electron capture in He++ H2collisions at intermediate impact energies

State-selective single electron capture in collisions of He${}^{+}$ with H${}_{2}$ molecules is investigated using the cold-target recoil-ion momentum spectroscopy technique. The energy range considered is 6.25 keV/amu (projectile velocity ${v}_{p}$ $=$ 0.5 a.u.) to 50 keV/amu (${v}_{p}$ $=$ 1.41 a.u.). In addition, we explore the transverse recoil momentum distributions that provide direct access to the angular scattering of the receding projectile. The present experimental data are contrasted to the theoretical results obtained by means of the classical trajectory Monte Carlo model with which we find good overall agreement in the energy range explored.