Laser-assisted (e,2e) study with twisted electron beam on H-atom

We numerically investigate the dynamics of inward circular finite-energy Airy beams carrying different orbital angular momentum (OAM) numbers in a close-Λ three-level atomic vapor with the electromagnetically induced transparency (EIT) window. We report that due to the EIT induced by the microwave field, the transverse intensity distribution properties of Airy beam can be feasibly manipulated and modulated through adjusting OAM numbers l and the frequency detuning, as well as the propagation distance, in the multi-level atomic systems. What’s more, the rotation of the beam also can be observed with different positions in atomic ensembles. The investigation may provide a useful tool for studying particle manipulation, signal processing and propagation in graded-index (GRIN) fibers.

The rich structure of transverse spatial modes of structured light has facilitated their extensive applications in quantum information and optical communication. The Laguerre–Gaussian (LG) modes, which carry a well-defined orbital angular momentum (OAM), consist of a complete orthogonal basis describing the transverse spatial modes of light. The application of OAM in free-space optical communication is restricted due to the experimentally limited OAM numbers and the complex OAM recognition methods. Here, we present a novel method that uses the advanced deep learning technique for LG modes recognition. By discretizing the spatial modes of structured light, we turn the OAM state regression into classification. A proof-of-principle experiment is also performed, showing that our method effectively categorizes OAM states with small training samples and the accuracy exceeds 99% from three-dimensional (3D) to fifteen-dimensional (15D) space. By assigning each category a classical information, we further apply our approach to an image transmission task, achieving a transmission accuracy of 99.58%, which demonstrates the ability to encode large data with low OAM number. This work opens up a new avenue for achieving high-capacity optical communication with low OAM number based on structured light.

The three-body distorted-wave Born approximation is used to calculate the (e,2e) triple differential cross sections (TDCSs) of Ag+(4p10) and Ag+(4d10) in different kinematical variables in coplanar asymmetric geometry. The angles 4, 10 and 20 are selected as the scattering electron angles. We find that the position of binary peak or the dip between split peaks are not in the direction of momentum transfer, which is probably ascribed to one kind of double-binary collision. We also find that the binary peaks show abnormal splits for Ag+(4p10). Such abnormal splits indicate that an (e,2e) process for inner valence orbital of ionic target becomes more complicated than for outer valence orbital. Furthermore, beside the binary peak and the recoil peak, some pronounced peaks appear at certain ejected angles in the (e,2e) TDCSs of Ag+(4p10) and Ag+(4d10). We consider that these pronounced peaks are probably related to one kind of double-binary collision.

Distorted-wave calculations of the triple differential cross section (TDCS) are presented for electron and positron impact ionization of Ar(3p) in coplanar asymmetric geometry at an impact energy of 1 keV and are compared with a recent experiment. The experiment indicates that the positron TDCS is generally larger than the equivalent electron TDCS. It is shown that the magnitude of the TDCS is extremely sensitive to the energy of the ejected electron and that only when the cross section is averaged over energy do we get a reasonable agreement with experiment.

In traditional scattering theory, the incident projectile is assumed to have an infinite coherence length. However, over the last decade, experimental and theoretical studies of collisions using heavy ion projectiles have shown that this assumption is not always valid. This has led to a growing number of studies that specifically examine the effects of the projectile's coherence length on collision cross sections. These studies have used heavy ion projectiles because they offer a straightforward method to control the projectile's coherence length through its momentum, and using these techniques, it has been demonstrated that the projectile's coherence length alters the cross sections. In contrast, it is widely presumed that the coherence length of an electron projectile is always sufficiently large that any effects on the cross sections can be safely neglected. We show that, contrary to this prevailing opinion, coherence effects are observable for electron projectiles and they can be controlled. We calculate triple differential cross sections (TDCSs) for ionization of ${\mathrm{H}}_{2}^{+}$ using twisted electron projectiles in the form of Laguerre-Gauss and Bessel electrons. Effects of the projectile's coherence length are observed through the presence or absence of two-slit interference features in the TDCSs. When the electron projectile's coherence length is large, ionization occurs from either nuclear center of the molecule, and two-slit interference features are visible in the TDCSs. In contrast, when the projectile's coherence length is small, ionization occurs from only one nuclear center and the TDCSs resemble those for ionization of atomic hydrogen. We demonstrate that the intrinsic parameters of the vortex projectiles, such as beam waist and opening angle, can be used to control the coherence length of electron projectiles.

In this letter, we have put out a fresh idea for managing the diffraction sample of optical vortex light that was transmitted from a four-level quantum dot molecule. We describe the creation of a new weak laser field via inter-dot tunneling, which causes the diffraction grating to be dependent on the orbital angular momentum (OAM) of the optical vortex light. We found that the relative phase between the implemented lights and the OAM number of the vortex light affect the intensity distribution of the asymmetric grating. Additionally, we discovered that the maximum amount of probe energy could be dispersed in higher orders of diffracted angles that were negative and positive by modifying the inter-dot tunneling and OAM number.

The triple differential cross-sections for the ionization of hydrogen by electron impact in the presence of a laser field have been calculated in the coplanar asymmetric geometry by using the first Born approximation and the symmetric geometry by using the Coulomb-Born approximation at an incident electron energy of 250 eV. The variation of the triple differential cross-sections, for fixed values of the angles of scattering and ejection, is studied as a function of the linear polarization of the laser field. The changes are quite amenable to experimental investigation.

In this study, detailed experimental research of triple differential cross section (TDCS) measurements is performed to investigate single ionization dynamics for the 1t2 orbital of methane molecule by 250 eV electron impact. In our experiments, the outgoing electrons are simultaneously measured in coincidence in a coplanar asymmetric geometry with the scattering angles of 10° and 20°. Therefore, TDCS measurements are performed for two different values of momentum transfer (K ≈ 0.9 au and 1.5 au). A detailed analysis of the dependence of the TDCS versus the momentum transfer is reported here.

The triple differential cross sections (TDCSs) of electron-impact ionization for ions (Li+ (1s2) and K+ (3p6)) and atoms (He (1s2) and Ar (3p6)) have been calculated at coplanar asymmetric geometry using the distorted wave Born approximation method. The features of binary peaks in the TDCSs of ions are compared with those of corresponding atoms. Differences of positions of binary peaks between ions and atoms indicate that the usual single-binary encounter mechanism, which is a good description of the electron collision with atoms, cannot describe the electron collision with ions well. A double-binary encounter mechanism is proposed to describe the electron collision with ions.

The molecular distorted-wave Born approximation is proposed to study the (e, 2e) reaction for H2 targets. The wave functions of the incoming and outgoing electrons are obtained by solving the Lippmann–Schwinger equations, and the T-matrix in the Lippmann–Schwinger equations is calculated in a momentum space static-exchange-optical model. Triple differential cross sections are computed for incident energies of 100 and 250 eV in coplanar asymmetric geometry. Comparison of the present calculated results with the available experimental data in the literature reveals that there is good agreement.

Theoretical work has already established the existence of a light-induced torque acting on the centre of mass of an atom, ion or molecule immersed in twisted light, where the transition frequency is suitably detuned from that of the twisted light beam. The twisted beam carries <i>l</i> units of orbital angular momentum per photon, and the steady-state saturation form of the torque is also determined by the width of the upper state in the atomic transition. It has been shown that, to leading order, the transfer of orbital angular momentum can only occur between the twisted light and the centre of mass motion. We argue here that, for small linewidth, the full time-dependence of the torque is needed to account correctly for the dynamics of atoms in a twisted light beam. We outline the theoretical framework needed to derive this full time-dependence, applying the theory to the motion in a twisted light beam of Eu³⁺ ions, which possess a particularly narrow linewidth state. For relatively large linewidth, the steady-state forces and torque are appropriate, but the processes of cooling and trapping require the application of several suitably oriented twisted beams. The description of atomic motion in multiple twisted beams demands the application of special coordinate transformations. We show how to construct the appropriate transformation matrices to represent a twisted light beam propagating in an arbitrary direction, and we proceed to investigate the cooling and trapping of Mg⁺ ions in sets of pairs of counter-propagating twisted beams in two-dimensional and three-dimensional molasses configurations.

A simple model is proposed to study the ionization of the atomic hydrogen by fast election impact in coplanar asymmetric geometry, making use of the post form of the enery shell transition matrix element and the two-potential formula. By virtue of dividing the full kinetic energy operator, we obtain an approximate solution of the three body problem through the canceling of the motion of two-election mass and exponent factor of relative motion and the approximation of projectile plane wave. TDCS(triple differential cross section) is expressed by the product of two factors,the structure factor T2 and correlation one T12. In this article, the contribution of these factors is investigated using the method of asymptotic series and method.

Triple differential cross sections for electron impact ionisation of helium by 600 eV electrons have been measured and normalised to an absolute scale by extrapolating the generalised oscillator strength to zero momentum transfer. In this optical limit the triple differential cross sections can be expressed by the dipole transition matrix elements which are accurately known from photoionisation. The same cross sections have been calculated in the first Born approximation using quantum defect phaseshifts and standing-wave solutions for the ejected electron within a simple static potential approximation. Rather good agreement between this first-order theory and experiment is obtained for momentum transfer up to approximately 0.7 au, which contains a large fraction of all collisions leading to single ionisation. On the other hand, the experiments demonstrate the existence of higher-order effects for q>0.5 au, but a quantitative estimate of their importance for the calculation of triple differential cross sections is not yet possible.

Triple differential cross section for the near threshold single ionization of helium atoms for equal energy sharing

The single ionization triple differential cross sections (TDCS) of the Ar ($3p$) atoms are reported for the positron and electron impact at 1 keV. The calculated cross sections have been obtained using distorted wave Born approximation (DWBA) approach for the average ejected electron energies 13 and 26 eV at different momentum transfer conditions. The present attempt is helpful to probe the information on the TDCS trends for the particle-matter and antiparticle-matter interactions and to analyze the recent measurements [Phy. Rev. A 95, 062703 (2017)]. The binary electron emission is enhanced while the recoil emission is decreased for the positron impact relative to the electron impact in the DWBA calculation results. Systematic shift of peaks, shifting away from the momentum transfer direction for positron impact and shifting towards each other for electron impact, is observed with increasing momentum transfer.