Physical Sciences and Mathematics Commons^™

Manipulating Atomic Fragmentation Processes By Controlling The Projectile Coherence, Kisra N. Egodapitiya, Sachin D. Sharma, Ahmad Hasan, Aaron C. Laforge, Don H. Madison, Robert Moshammer, Michael Schulz

Physics Faculty Research & Creative Works

We have measured the scattering angle dependence of cross sections for ionization in p+H₂ collisions for a fixed projectile energy loss. Depending on the projectile coherence, interference due to indistinguishable diffraction of the projectile from the two atomic centers was either present or absent in the data. This shows that, due to the fundamentals of quantum mechanics, the preparation of the beam must be included in theoretical calculations. The results have far-reaching implications on formal atomic scattering theory because this critical aspect has been overlooked for several decades.

Preparing A Vacuum Chamber To Trap Atoms, And The Principles Of A Magneto-Optical Trap, Grant Rayner

Physics

No abstract provided.

Three-Body Dynamics In Single Ionization Of Atomic Hydrogen By 75 Kev Proton Impact, Ahmad Hasan, Michael Schulz, Aaron C. Laforge, Jason S. Alexander, M. F. Ciappina, M. A. Khakoo, Kisra Nayomal Egodapitiya

Physics Faculty Research & Creative Works

Doubly differential cross sections for single ionization of atomic hydrogen by 75 keV proton impact have been measured and calculated as a function of the projectile scattering angle and energy loss. This pure three-body collision system represents a fundamental test case for the study of the reaction dynamics in few-body systems. A comparison between theory and experiment reveals that three-body dynamics is important at all scattering angles and that an accurate description of the role of the projectile-target-nucleus interaction remains a major challenge to theory.

Quantitative Rescattering Theory For Laser-Induced High-Energy Plateau Photoelectron Spectra, Zhangjin Chen, Anh-Thu Le, Toru Morishita, C. D. Lin

Physics Faculty Research & Creative Works

A comprehensive quantitative rescattering (QRS) theory for describing the production of high-energy photoelectrons generated by intense laser pulses is presented. According to the QRS, the momentum distributions of these electrons can be expressed as the product of a returning electron wave packet with the elastic differential cross sections (DCS) between free electrons with the target ion. We show that the returning electron wave packets are determined mostly by the lasers only and can be obtained from the strong field approximation. The validity of the QRS model is carefully examined by checking against accurate results from the solution of the time-dependent …

Imaging-Based Parametric Resonance In An Optical Dipole-Atom Trap, S. Balik, A. L. Win, M. D. Havey

Physics Faculty Publications

We report sensitive detection of parametric resonances in a high-density sample of ultracold ⁸⁷Rb atoms confined to a far-off-resonance optical dipole trap. Fluorescence imaging of the expanded ultracold atom cloud after a period of parametric excitation shows significant modification of the atomic spatial distribution and has high sensitivity compared with traditional measurements of parametrically driven trap loss. Using this approach, a significant shift of the parametric resonance frequency is observed and attributed to the anharmonic shape of the dipole trap potential. 2009 The American Physical Society.

Quantitative Rescattering Theory For Nonsequential Double Ionization Of Atoms By Intense Laser Pulses, Samuel Micheau, Zhangjin Chen, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

Laser-induced electron recollisions are fundamental to many strong field phenomena in atoms and molecules. Using the recently developed quantitative rescattering theory, we demonstrate that the nonsequential double ionization (NSDI) of atoms by lasers can be obtained quantitatively in terms of inelastic collisions of the target ions with the free returning electrons where the latter are explicitly given by a spectrum-characterized wave packet. Using argon atoms as target, we calculated the NSDI yield including contributions from direct (e,2e) electron-impact ionization and electron-impact excitation accompanied by subsequent field ionization. We further investigate the dependence of total NSDI on the carrier-envelope phase of …

Retrieving Photorecombination Cross Sections Of Atoms From High-Order Harmonic Spectra, Shinichiro Minemoto, Toshihito Umegaki, Yuichiro Oguchi, Toru Morishita, Anh-Thu Le, Shinichi Watanabe, Hirofumi Sakai

Physics Faculty Research & Creative Works

We observe high-order harmonic spectra generated from a thin atomic medium, Ar, Kr, and Xe, by intense 800-nm and 1300-nm femtosecond pulses. A clear signature of a single-atom response is observed in the harmonic spectra. Especially in the case of Ar, a Cooper minimum, reflecting the electronic structure of the atom, is observed in the harmonic spectra. We successfully extract the photorecombination cross sections of the atoms in the field-free condition with the help of an accurate recolliding electron wave packet. The present protocol paves the way for exploring ultrafast imaging of molecular dynamics with attosecond resolution.

Reexamining Blackbody Shifts For Hydrogenlike Ions, Ulrich D. Jentschura, Martin K. Haas

Physics Faculty Research & Creative Works

We investigate blackbody-induced energy shifts for low-lying levels of atomic systems, with a special emphasis on transitions used in current and planned high-precision experiments on atomic hydrogen and ionized helium. Fine-structure- and Lamb-shift-induced blackbody shifts are found to increase with the square of the nuclear charge number, whereas blackbody shifts due to virtual transitions decrease with increasing nuclear charge as the fourth power of the nuclear charge. We also investigate the decay width acquired by the ground state of atomic hydrogen, due to interaction with blackbody photons. The corresponding width is due to an instability against excitation to higher excited …

Efimov States Embedded In The Three-Body Continuum, Nirav P. Mehta, Seth T. Rittenhouse, J P. D’Incao, Chris H. Greene

Physics and Astronomy Faculty Research

We present analytical solutions for the three-body problem with multichannel interactions and identify a class of quasibound Efimov states that can be viewed as three-body Fano-Feshbach resonances. Our method employs a multichannel generalization of the Fermi pseudopotential to model low-energy atom-atom interactions near a magnetically tunable Fano-Feshbach resonance. We discuss the conditions under which quasibound Efimov states may be supported and identify the interaction parameters that limit the lifetimes of these states. We speculate that it may be possible to observe these states using spectroscopic methods, perhaps allowing for the measurement of multiple Efimov resonances.

Extraction Of The Species-Dependent Dipole Amplitude And Phase From High-Order Harmonic Spectra In Rare-Gas Atoms, Anh-Thu Le, Toru Morishita, C. D. Lin

Physics Faculty Research & Creative Works

Based on high-order harmonic generation (HHG) spectra obtained from solving the time-dependent Schrödinger equation for atoms, we established quantitatively that the HHG yield can be expressed as the product of a returning electron wave packet and photorecombination cross sections, and the shape of the returning wave packet is shown to be largely independent of the species. By comparing the HHG spectra generated from different targets under identical laser pulses, accurate structural information, including the phase of the recombination amplitude, can be retrieved. This result opens up the possibility of studying the target structure of complex systems, including their time evolution, …

Potential For Ultrafast Dynamic Chemical Imaging With Few-Cycle Infrared Lasers, Toru Morishita, Anh-Thu Le, Zhangjin Chen, C. D. Lin

Physics Faculty Research & Creative Works

We studied the photoelectron spectra generated by an intense few cycle infrared laser pulse. By focusing on the angular distributions of the back rescattered high energy photoelectrons, we show that accurate differential elastic scattering cross-sections of the target ion by free electrons can be extracted. Since the incident direction and the energy of the free electrons can be easily changed by manipulating the laser's polarization, intensity and wavelength, these extracted elastic scattering cross-sections, in combination with more advanced inversion algorithms, may be used to reconstruct the effective single-scattering potential of the molecule, thus opening up the possibility of using few-cycle …

Detectability Of Dissipative Motion In Quantum Vacuum Via Superradiance, Woo-Joong Kim, James Hayden Brownell, Roberto Onofrio

Dartmouth Scholarship

We propose an experiment for generating and detecting vacuum-induced dissipative motion. A high frequency mechanical resonator driven in resonance is expected to dissipate mechanical energy in quantum vacuum via photon emission. The photons are stored in a high quality electromagnetic cavity and detected through their interaction with ultracold alkali-metal atoms prepared in an inverted population of hyperfine states. Superradiant amplification of the generated photons results in a detectable radio- frequency signal temporally distinguishable from the expected background.

Simple Plane Wave Implementation For Photonic Crystal Calculations, Shangping Guo, Sacharia Albin

Electrical & Computer Engineering Faculty Publications

A simple implementation of plane wave method is presented for modeling photonic crystals with arbitrary shaped ‘atoms’. The Fourier transform for a single ‘atom’ is first calculated either by analytical Fourier transform or numerical FFT, then the shift property is used to obtain the Fourier transform for any arbitrary supercell consisting of a finite number of ‘atoms’. To ensure accurate results, generally, two iterating processes including the plane wave iteration and grid resolution iteration must converge. Analysis shows that using analytical Fourier transform when available can improve accuracy and avoid the grid resolution iteration. It converges to the accurate results …

Ionization Of Hydrogen Atoms By Fast Electrons, Sindu P. Jones, Don H. Madison

Physics Faculty Research & Creative Works

We study ionization of atomic hydrogen by fast electrons using asymptotically correct two-center wave functions to describe the scattering system both initially and finally. For the final state, we employ the well-known product wave function of Redmond, which treats all three two-body Coulomb interactions exactly, albeit independently. This "3C" wave function is the leading term of the exact scattering wave function, regardless of how slow the three particles are, if any two particles have large relative separation [Y.E. Kim and A.L. Zubarev, Phys. Rev. A 56, 521 (1997)]. Here we extend the analysis of Qiu et al. [Phys. Rev. A …

Short-Pulse Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story

Physics Faculty Research & Creative Works

Atoms in doubly excited states above the first ionization limit can decay via autoionization in which an electron is emitted leaving an ion, or by photoemission which leaves the atom in a singly excited state. In this paper, it is demonstrated that interaction between the atoms and a laser pulse that is short compared to the autoionization lifetime can lead to large enhancement of the photoemission process by stimulating the atoms to emit a photon. Since the resultant singly excited atoms do not autoionize, this process can be viewed as an enhancement of the stabilization of the doubly excited atoms …

Structure And Interaction Energies Of Kr Atoms Adsorbed On Graphitic Amorphous Carbon, Sang -Joon Lee

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The physisorption of Kr on graphitic amorphous carbon (g-C) has been investigated using a statistical approach. The interaction energy calculation process (i) established a structural model of g-C and (ii) determined the adsorbate-adsorbate and the adsorbate-substrate interaction potentials on g-C.

The structural model of g-C was divided into three regions. For the interaction potential between a Kr atom and a carbon atom the short and medium range order of g-C was described with a discrete medium model based on three ring clusters using ring statistics from Beeman's continuous random network C1120 model of g-C. For the intermediate distance region, Beeman's …

Landau-Zener Treatment Of Intensity-Tuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher

Physics Faculty Research & Creative Works

When exposed to intense light of ~580 nm, the ground state of K shifts up in energy, passing through two photon resonances with Rydberg states, and finally crossing the two-photon ionization limit. We have used laser pulses of varying duration to study the nature of the population transfer from the ground state to the excited state due to the intensity-tuned resonances encountered during the rising edge of the pulse. A dynamic Floquet approach in which the resonances are treated as avoided crossings of the Floquet energy levels is used to model the population transfer and gives excellent agreement with the …

Energetic Protons And Deuterons Emitted Following Μ⁻ Capture By ³He Nuclei, W. J. Cummings, G. E. Dodge, S. S. Hanna, B. H. King, S. E. Kuhn, Y. M. Shin, R. Helmer, R. B. Schubank, N. R. Stevenson, U. Wienands, Y. K. Lee, G. R. Mason, B. E. King, K. S. Chung, J. M. Lee, D. P. Rosenzweig

Physics Faculty Publications

Spectra of energetic protons and deuterons emitted following negative muon capture from rest in ³He have been measured for the first time. Significant capture strength is observed at high energy transfers (mμ- E_v >60 MeV) for the two-body and three-body breakup channels, indicative of the importance of nucleon-nucleon correlations and meson exchange currents in the capture process. A simple plane wave impulse approximation calculation reproduces the proton spectrum reasonably well, but underpredicts the deuteron rate at the highest energies by a large factor.

Density Effect In Cu K-Shell Ionization By 5.1-Gev Electrons, W. E. Meyerhof, D. G. Jensen, D. M. Kawall, S. E. Kuhn, D. W. Spooner, Z. E. Meziani, D.. N. Faust

Physics Faculty Publications

We have made an absolute measurement of the Cu K-shell impact ionization cross section by 5.1-GeV electrons, which demonstrates directly a density effect predicted by Fermi in 1940. By determining the ratio of the K x-ray yield from a thin front and back layer of the target by a novel grazing emission method, we have verified the effect of transition radiation on the x-ray production, suggested by Sorensen and reported by Bak et al.