Atomic, Molecular and Optical Physics Commons^™

Guiding Fast Ion Beam By Suppressing Secondary Ions, Yingli Xue, Junliang Liu, Mingwu Zhang, Daniel Fischer, Guoxing Xia, Nikolaus Stolterfoht, Reinhold Schuch, Yehong Wu, Bian Yang, Xiaoxiao Li, Caojie Shao, Wei Wang, Zhangyong Song, Xing Fang

Physics Faculty Research & Creative Works

We demonstrate that secondary ions sputtered from a macrocapillary's inner surface by the primary beam induce premature saturation of the guiding field, hindering fast ion guiding. By suppressing secondary ion sputtering with grooved surfaces, we achieve a guiding-field potential difference exceeding 1 kV, 2 orders of magnitude larger than previously achieved in stable ion guiding. This enables stable guiding of a 20-keV/q O5+ beam at offset angles up to 15°, with transmitted ions retaining their initial energy and charge state. A self-consistent field model accurately reproduces these results, revealing that guiding performance relies on managing secondary ions and the channel's …

First Remi Experiments At A Cryogenic Ion Storage Ring, M. Schulz, F. Herrmann, W. Zhang, A. Dorn, M. Grieser, F. Grussie, H. Kreckel, O. Novotny, A. Wolf, T. Pfeifer, C. D. Schröter, R. Moshammer

Civil, Architectural and Environmental Engineering Faculty Research & Creative Works

We have recorded double, triple, and quadruple coincidences between neutralized projectiles, recoiling target ions, and two electrons created in collisions of slow anions with neutral atoms. The experiments were performed at the cryogenic storage ring in Heidelberg. The recoil ions and ejected electrons were momentum-analyzed using a Reaction Microscope (ReMi) spectrometer. Various processes involving electron detachment from the projectile accompanied by various transitions in the target were investigated. Detachment without any transition in the target is qualitatively well described by a quasi-free electron model in the case of an Ar target. In detachment with single target ionization, no signatures of …

Fully Differential Studies On Dissociative Capture In P + D2 Collisions And On Ionization In P + He Collisions, Shruti Majumdar

Doctoral Dissertations

Advancing our understanding of few-body dynamics in simple atomic systems is a fundamental objective in atomic scattering research. The underlying problem is that the Schrödinger equation is not analytically solvable for more than two mutually interacting particles. This involves a comprehensive exploration of various channels, such as ionization, capture, and excitation. A common theoretical approach to describe ion-atom collisions is based on perturbation theory, where the scattering amplitude is expanded in powers of the interaction potential. Here, understanding the few-body problem means accurately describing the relative importance of the higher- vs the first order terms.

In the case of ionization, …

Time-Resolved 3d Momentum Spectroscopy In Continuous Wave Atomic Photoionization Experiments, K. L. Romans, B. P. Acharya, A. H.N.C.De Silva, K. Foster, O. Russ, Daniel Fischer

Physics Faculty Research & Creative Works

An experimental continuous-wave (cw) pump-probe scheme is demonstrated by investigating the population and photoionization dynamics of an atomic system. In particular, 6Li atoms are initially prepared in optically pumped 22S1/2 and 22P3/2 states before being excited via multi-photon absorption from a tunable femtosecond laser. The subsequent cascade back to the ground state is analyzed by ionizing the atoms in the field of a cw optical dipole trap laser. Conventional spectroscopic methods, such as standard cold-target recoil ion momentum spectroscopy or velocity map imaging, cannot provide simultaneous momentum and time-resolved information on an event-by-event basis for the system investigated here. The …

Coupled-Channel Calculations Of Fully Differential Cross Sections For Ionization In 75-Kev P + He Collisions, K. H. Spicer, N. W. Antonio, M. S. Schöffler, Michael Schulz, A. S. Kadyrov

Physics Faculty Research & Creative Works

The fully differential cross section is the most detailed quantity that can be measured or calculated to study ionization in few-body systems. For 75 keV proton collisions with helium, various experimental data are available. However, previous theoretical calculations found significant discrepancies across the entire range of data. In this work the wave-packet convergent close-coupling method is extended to calculating these cross sections for electrons ejected with energies from 1 to 75.4 eV. The approach utilizes a two-center expansion and correlated two-electron helium wave functions to describe the four-body proton-helium system. While there is good agreement with the experiment for electrons …

Multiply Differential Study Of Detachment With Simultaneous Target Excitation In Anion-Atom Collisions, M. Schulz, F. Herrmann, W. Zhang, D. V. Chicharro, A. Dorn, M. Grieser, F. Grussie, H. Kreckel, O. Novotny, F. Trost, A. Wolf, T. Pfeifer, C. D. Schröter

Physics Faculty Research & Creative Works

We have measured momenta of electrons and recoil ions in triple coincidence with neutralized projectiles for slow collisions between various anions and target atoms. From the data we extracted triple differential momentum and angular distributions of electrons ejected in detachment, in detachment with simultaneous target ionization (DI), and in detachment with simultaneous target excitation (DE). The DI rates relative to the DE rates depend sensitively on the projectile speed and on the properties of the target.

Continuous Pump-Probe Experiment To Observe Zeeman Wave-Packet Dynamics, K. L. Romans, K. Foster, S. Majumdar, B. P. Acharya, O. Russ, A. H.N.C. De Silva, Daniel Fischer

Physics Faculty Research & Creative Works

In this work, we study the coherent dynamics of an atomic Zeeman wave packet using a continuous pump-probe scheme. A polarized Zeeman wave packet is created in laser-cooled lithium atoms via few-photon excitation by a femtosecond laser pulse, producing a state with a magnetic moment tilted relative to an external magnetic field. The subsequent Larmor precession of the atomic magnetic moment is probed via continuous ionization by an optical dipole trap (ODT) laser. The resulting ionization fragments—photoelectrons and photo ions—are detected in coincidence using a cold target recoil ion momentum spectrometer (COLTRIMS). While the ODT facilitates further cooling of the …

Momentum Imaging Of Electrons And Recoil Ions From Anion-Neutral Interactions In A Cryogenic Ion Storage Ring, F. Herrmann, W. Zhang, M. Schulz, D. V. Chicharro, A. Dorn, M. Grieser, F. Grussie, H. Kreckel, O. Novotny, F. Trost, A. Wolf, T. Pfeifer, C. D. Schröter

Physics Faculty Research & Creative Works

We have momentum-analyzed electrons and recoil ions in triple coincidence with projectiles neutralized in 300-keV Si-+Ar collisions. The experiment was performed at a cryogenic ion storage ring with an in-ring reaction microscope. Differential momentum distributions for detachment with simultaneous target ionization were obtained. At more than 15% of the detachment-only rate the ionization rate is surprisingly large. A correlated two-electron channel is found to be dominant. This is also unexpected because the projectile energy is well below the threshold for the correlated process.

Photoionization Of Spin-Polarized Rydberg Atoms Out Of A Continuous Wave Optical Dipole Trap, Kevin Lee Romans

Doctoral Dissertations

"Recent research has demonstrated the need for a fully differential experiment on the photoionization of ⁶Li Rydberg atoms in a continuous wave (cw) laser field, as this would provide a new path forward for studying never before accessible atom-light interactions. Rydberg atoms are back in the focus of intense research due to their peculiar properties, which make them interesting candidates for quantum optics and information applications. In this work, we study the ionization of such Rydberg atoms, due to their interaction with a trapping laser field, by utilizing a reaction microscope (ReMi) capable of measuring photoelectron momentum distributions with …

Using Coherence And Interference To Study The Few Body Dynamics In Simple Atomic Collisions Systems, Sujan Bastola

Doctoral Dissertations

"Atomic Collision experiments are best suited to sensitively test the few-body dynamics of simple systems. The few-body dynamics, in turn, can be sensitively affected by interference effects. However, an important requirement to observe interference effects in atomic scattering experiments is that the incoming projectile beam must be coherent. The coherence properties of the incoming projectile can be controlled by the geometry of the collimating slit placed before the target. We performed a kinematically complete experiment where a 75 keV proton beam is crossed with a molecular hydrogen beam to study the dissociative capture process. The motivation for this project was …

Reaction Microscope For Investigating Ionization Dynamics Of Weakly Bound Alkali Dimers, N. Kurz, Daniel Fischer, T. Pfeifer, A. Dorn

Physics Faculty Research & Creative Works

We report on the implementation of a far-off-resonant, optical dipole force trap in a reaction microscope combined with a magneto-optical trap. Kinematically complete multi-photon ionization experiments were performed on optically trapped 6Li atoms and photo-associated 6Li2 molecules in their highest vibrational state. The apparatus allows us to distinguish different ionization mechanisms related to the presence of the IR field of the optical dipole trap that can occur during ionization of 6Li and 6Li2 in strong fields. In a series of proof-of-principle experiments, we detect weakly bound dimers via three-photon ionization with femtosecond pulses (τ = 30 fs) at a central …

Complete Experiments On Multi-Photon Ionizations Of Ultra-Cold And Polarized Atoms, Bishnu Prasad Acharya

Doctoral Dissertations

“Fundamental atomic processes such as collision-induced ionization are of relevance in many scientific fields. Describing these reactions can still pose a substantial challenge due to the well-known “few-body problem”, which entails that there is no analytical solution of the equations of motion for systems of more the 2 mutually interacting particle. Novel experimental tools and advancements in theorical methods enable to obtain detailed information on atomic dynamics providing insight into both, the phase as well as the amplitude of the quantum-mechanical wave functions of the particles. In this project, we developed experimental techniques studying multi-photon ionization of lithium in femto-second …

Triple-Differential Cross Sections For (E,2e) Electron-Impact Ionization Dynamics Of Tetrahydrofuran At Low Projectile Energy, Enliang Wang, Xueguang Ren, Maomao Gong, Esam Ali, Zhenpeng Wang, Chao Ma, Don H. Madison, Xiangjun Chen, Alexander Dorn

Physics Faculty Research & Creative Works

We study the triple-differential cross section (TDCS) for the electron-impact ionization of the highest occupied molecular orbital of tetrahydrofuran at a projectile energy E0=91eV. The experimental data were measured using a reaction microscope, which covers a large part of the full solid angle for the secondary electron emission with energies ranging from 6 to 15 eV, and projectile scattering angles ranging from -10° to -20°. The experimental TDCSs are internormalized across all measured scattering angles and ejected energies. They are compared with predictions from the multicenter distorted-wave (MCDW) approximation and a modified MCDW-Nee method which includes the post collision interaction …

Fully Differential Study Of Ionization Of H2 By P Impact Near Velocity Matching, M. Dhital, S. Bastola, A. Silvus, A. Hasan, B. R. Lamichhane, E. Ali, M. F. Ciappina, R. A. Lomsadze, D. Cikota, B. Boggs, Don H. Madison, Michael Schulz

Physics Faculty Research & Creative Works

Fully differential cross sections (FDCS) for ionization in p + H2 collisions in the region of the electron-projectile velocity matching were measured and calculated. The FDCS were found to be very sensitive to the details of the few-body dynamics underlying the reaction.

New Structures In Fully Differential Cross Sections For Ionization Of He By Proton Impact, M. Dhital, S. Bastola, A. Silvus, A. Hasan, B. R. Lamichhane, E. Ali, M. F. Ciappina, R. A. Lomsadze, Don H. Madison, Michael Schulz

Physics Faculty Research & Creative Works

Fully differential cross sections (FDCS) for ionization in p + He collisions were measured and calculated for several projectile energy losses. The electron angular dependence of the FDCS reveals structures not seen in previous studies.

Triple Differential Cross Sections For Electron Impact Ionization Of Methane At Intermediate Energy, C. Granados, E. Ali, A. Sakaamini, M. Harvey, L. U. Ancarani, A. J. Murray, M. Dogan, C. Ning, J. Colgan, Don H. Madison

Physics Faculty Research & Creative Works

In a joint experimental and theoretical collaboration, triple differential cross sections are presented for electron-impact single ionization of the 1t2 and 2a1 states of CH4 at an incident electron energy of 250 eV. Experimental data from two different laboratories are compared with molecular 3-body distorted wave (M3DW) and generalized Sturmian function (GSF) calculations. Overall, we find a good experiment-experiment, and also a relatively good experiment-theories, agreement. We observe that for the 1t2 state, similarly to ionization of atomic p-states, the peak is sometimes doubled.

Energy Dependent Relative Cross Sections In Carbon 1s Photoionization, Michael Schulz, A. Hasan, B. Lamichhane, T. Arthanayaka, M. Dhital, S. Bastola, D. Céolin, C. Nicolas, T. Marchenko, G. Goldsztejn, L. Journel, R. Guillemin, T. X. Carroll, K. J. Børve

Physics Faculty Research & Creative Works

Synopsis We demonstrate that the possibility of monitoring relative photoionization cross sections over a large photon energy range extending to hard x-rays allows studying and disentangling shake processes and intramolecular inelastic scattering effects. An "EXAFS"-type of oscillatory behavior of the relative C 1s cross sections is observed in a wide photon energy range up to 1 keV due to multiple intramolecular elastic scattering of the photoelectron. These effects are also present in solids and constitute a significant part of all elastic and inelastic scattering effects occurring in solids.

Deep Minima In The Triply Differential Cross Section For Ionization Of Atomic Hydrogen By Electron And Positron Impact, C. M. Demars, S. J. Ward, J. Colgan, S. Amami, Don H. Madison

Physics Faculty Research & Creative Works

We investigate ionization of atomic hydrogen by electron-and positron-impact. We apply the Coulomb-Born (CB1) approximation, various modified CB1 approximations, the three-body distorted wave (3DW) approximation, and the time-dependent close-coupling (TDCC) method to electron-impact ionization of hydrogen. For electron-impact ionization of hydrogen for an incident energy of approximately 76.45 eV, we obtain a deep minimum in the CB1 triply differential cross section (TDCS). However, the TDCC for 74.45 eV and the 3DW for 74.46 eV gave a dip in the TDCS. For positron-hydrogen ionization (breakup) we apply the CB1 approximation and a modified CB1 approximation. We obtain a deep minimum in …

Molecular-Frame (E, 2e) Ionization Dynamics Of H2 At High Impact-Energy, Enliang Wang, Esam Ali, Xingyu Li, Xueguang Ren, Xiangjun Chen, Don H. Madison, Alexander Dorn

Physics Faculty Research & Creative Works

Abstract: We report a combined experimental and theoretical study on the electron-impact ionization dynamics of H2 at an impact-energy of 520 eV. The molecular-frame fivefold-differential cross sections were measured for electron emission in the plane perpendicular to the incoming projectile beam. An (e, 2e + ion) triple coincidence method was used covering projectile scattering angles of 6.5°, 10.0° and 20.0° and ejected energies of 20 eV and 30 eV. The experimental cross sections are compared with results from the multi-center distorted-wave (MCDW) as well as the molecular three-body distorted wave (M3DW) approaches. M3DW is in overall better agreement with the …

Fully Differential Study Of Higher-Order Contributions To The Few-Body Dynamics Of Simple Atomic Systems, Madhav Dhital

Doctoral Dissertations

”Advancing our understanding of the few-body dynamics in simple atomic systems is one of the most important goals of atomic scattering research. In perturbation theory, this goal entails accurately describing the relative contributions from first versus higher-order mechanisms. One higher-order mechanism that is particularly important for target ionization by a charged-particle impact is known as post-collision interaction (PCI). There, the projectile and the ejected electron interact with each other at least twice. In the first interaction, the projectile transfers sufficient energy for the electron to be lifted to the continuum. The second interaction occurs in the outgoing part of the …

Electron Transfer Plus Double Ionization In Slow He2+ + Ar Collisions, Y. Gao, Michael Schulz, D. L. Guo, S. F. Zhang, X. L. Zhu, R. T. Zhang, W. T. Feng, D. M. Zhao, X. Ma

Physics Faculty Research & Creative Works

We performed a kinematically complete experiment on double ionization accompanied by single capture in 30 keV/amu He2⁺ + Ar collisions. The data were systematically analyzed using three different techniques, namely, fully differential cross sections as a function of the electron emission angle of each electron, the correlation function, and four-particle Dalitz plots. The data can to a large extent be explained within the independent electron model. However, the correlation function reveals small but significant effects from correlations in the initial target state. These correlations strongly depend on the interaction between the nuclei of the collision partners. Furthermore, a surprisingly …

Signatures Of Autoionization In The Angular Electron Distribution In Two-Photon Double Ionization Of Ar, S. Augustin, Michael Schulz, G. Schmid, K. Schnorr, E. V. Gryzlova, H. Lindenblatt, S. Meister, Y. F. Liu, F. Trost, L. Fechner, A. N. Grum-Grzhimailo, S. M. Burkov, M. Braune, R. Treusch

Physics Faculty Research & Creative Works

A kinematically complete experiment on two-photon double ionization of Ar by free-electron laser radiation with a photon energy of 27.93 eV was performed. The electron energy spectra show that double ionization is dominated by the sequential process. Comparison of the electron angular distributions to our data for single ionization and to theory confirms that even in the sequential process the electrons from both ionization steps are correlated with each other through polarization of the intermediate Ar+ state. Furthermore, a very important role of autoionization in both ionization steps is found.

Probing Scattering Phases Via Two-Center Interferences In Collisions Of He²⁺ On Co, Y. Gao, S. F. Zhang, X. L. Zhu, D. L. Guo, Michael Schulz, A. B. Voitkiv, D. M. Zhao, B. Hai, M. Zhang, R. T. Zhang, W. T. Feng, S. Yan, H. B. Wang, Z. K. Huang

Physics Faculty Research & Creative Works

Phases of quantum transition amplitudes contain very important information about physical processes. However, as a rule, they may not be accessed experimentally. This is, in particular, the case when collisions of ions and atoms are studied. In this rapid communication, we explore double electron capture in collisions of α particles with CO molecules. Regarding the atomic cores of the molecule as two "slits," we show that atomic "double slit" interference can be exploited to experimentally extract information about phases of the projectile scattering on the cores.

Theoretical Calculations For Electron Impact Ionization Of Atoms And Molecules, Sadek Mohamed Fituri Amami

Doctoral Dissertations

"In the last twenty years, significant progress has been made for the theoretical treatment of electron impact ionization (e,2e) of atoms and molecules and, for some cases, very nice agreement between experiment and theory has been achieved. In particular, excellent agreement between theory and experiment and theory has been achieved for ionization of hydrogen and helium. However, agreement between experiment and theory is not nearly as good for ionization of larger atoms and molecules. In the first part of this dissertation, different theoretical approaches will be employed to study the triply differential cross section (TDCS) for low and intermediate energy …

Fully Differential Study Of Projectile Coherence Effects In Ionization Of Molecular Hydrogen And Atomic Helium, Thusitha Priyantha Arthanayaka

Doctoral Dissertations

"It has been well established, that projectile coherent properties are important for the study of atomic fragmentation processes. Recent studies of ionization of molecular hydrogen had demonstrated that measured double differential cross sections (DDCS) are very sensitive to the coherent length of the projectile. These measurements have been performed with varied coherence length of the projectiles by controlling the geometry of the collimating slits, which are placed before the target. Later, fully differential cross sections (FDCS) for a coherent and an incoherent projectile beam has been study for the same collision system and the results confirmed the important role of …