Atomic, Molecular and Optical Physics Commons^™

Comparison Of Absorption, Fluorescence, And Polarization Spectroscopy Of Atomic Rubidium, Seth T. Ashman, Cayla Stifler, Joaquin Romero

Engineering & Physics Faculty Publications

An ongoing spectroscopic investigation of atomic rubidium utilizes a two-photon, single-laser excitation process. Transitions accessible with our tunable laser include 5P1/2 (F ′ ) ← 5S1/2 (F) and 5P3/2 (F ′ ) ← 5S1/2 (F). The laser is split into a pump and probe beam to allow for Doppler-free measurements of transitions between hyperfine levels. The pump and probe beams are overlapped in a counter-propagating geometry and the laser frequency scans over a transition. Absorption, fluorescence and polarization spectroscopy techniques are applied to this basic experimental setup. The temperature of the vapor cell and the power of the pump and …

Imaging The Dipole-Dipole Energy Exchange Between Ultracold Rubidium Rydberg Atoms, Donald P. Fahey, Thomas J. Carroll, Michael W. Noel

Physics and Astronomy Faculty Publications

The long-range, anisotropic nature of the interaction among atoms in an ultracold dipolar gas leads to a rich array of possibilities for studying many-body physics. In this work, an ultracold gas of highly excited atoms is used to study energy transport due to the long-range dipole-dipole interaction. A technique is developed to measure both the internal energy states of the interacting Rydberg atoms and their positions in space. This technique is demonstrated by observing energy exchange between two spatially separated groups of Rydberg atoms excited to two different internal states. Simulations confirm the general features of the energy transport in …

Electron Transmission Through Micrometer Sized Funnelshaped Tapered Glass Capillaries And Electron Micro-Beam Production, Samanthi Jayamini Wickramarachchi

Dissertations

The prime motivation of this work is to understand the fundamental transmission process of an electron beam through a funnel-shaped capillary taking into account its shape together with the energy, angular and time dependence of the transmitted electrons produce a microsized electron beam. The utilized capillaries had inlet/outlet diameters of 800/16 μm, 800/100 μm and lengths of 35 mm. Considerable transmission of 800 and 1000 eV electrons for tilt angles up to 1.5^o and only small transmission for 500 eV electrons was observed for the capillary with the smaller outlet diameter of 16 μm. Incident electrons with energies of …

Modelling Transient Terahertz Magneto-Spectroscopy Measurements Of P-Type Cvd Graphene Leading To A Negative Photoconductivity., Rhyan Foo Kune

Macalester Journal of Physics and Astronomy

Ultrafast Terahertz (THz) Magneto-Spectroscopy (UTMS) measurements were performed on p-type CVD graphene sample to investigate the intrinsic carrier dynamics of the material. We investigated static and time-resolved THz transmission measurements, in which the sample was photo-excited by a near infrared (NIR) pump pulse, in order to study its behavior in a magnetic field. In these measurements the free carriers were probed to independently measure the carrier density and scattering rate in this film. We observed, in our graphene sample, an increase in transmission related to a negative photoconductivity (decrease in conductivity after photoexcitation) consistent with previous research. This decrease is …

Modeling The Optical Response To A Near-Field Probe Tip From A Generalized Multilayer Thin Film, A.J. Lawrence

Dissertations and Theses

The contrast mechanism in Kerr imaging is the apparent angle through which the plane of polarization is rotated upon reflection from a magnetic surface. This can be calculated for a well characterized surface given the polarization state of the incident light. As in traditional optical microscopy, the spatial resolution is limited by diffraction to roughly half the wavelength of the illumination light.

The diffraction limit can be circumvented through the use of near-field scanning optical microscopy, in which the illumination source is an evanescent field at the tip of a tapered optical fiber. A novel probe design for near-field optical …

A Slow Neutron Polarimeter For The Measurement Of Parity-Odd Neutron Rotary Power, W. M. Snow, E. Anderson, L. Barron-Palos, C. D. Bass, T. D. Bass, Bret E. Crawford, C. Crawford, J. M. Dawkins, D. Esposito, J. Fry, H. Gardiner, K. Gan, C. Haddock, B. R. Heckel, A. T. Holley, J. C. Horton, C. Huffer, J. Lieffers, D. Luo, M. Maldonado-Velazquez, D. M. Markoff, A. M. Micherdzinska, H. P. Mumm, J. S. Nico, M. Sarsour, S. Santra, E. I. Sharapov, H. E. Swanson, S. B. Walbridge, V. Zhumabekova

Physics and Astronomy Faculty Publications

We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutronoptical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable ofmeasuring a neutron rotary power of dϕ/dz = 1 × 10⁻⁷ rad/m.

Interstitial Silicon Ions In Rutile Tio2 Crystals, Eric M. Golden, Nancy C. Giles, Shan Yang, Larry E. Halliburton

Faculty Publications

Electron paramagnetic resonance (EPR) is used to identify a new and unique photoactive silicon-related point defect in single crystals of rutile TiO₂. The importance of this defect lies in its assignment to interstitial silicon ions and the unexpected establishment of silicon impurities as a major hole trap in TiO₂. Principal g values of this new S=1/2 center are 1.9159, 1.9377, and 1.9668 with principal axes along the [¯110],[001], and [110] directions, respectively. Hyperfine structure in the EPR spectrum shows the unpaired spin interacting equally with two Ti nuclei and unequally with two Si nuclei. These silicon …

Measuring The Hyperfine Splittings Of Lowest Energy Atomic Transitions In Rubidium, Benjamin D. Graber

Undergraduate Honors Thesis Projects

The goal of this experiment was to measure the hyperfine energy splittings of the ground to first excited state transitions in rubidium using saturated absorption spectroscopy. Using this technique, we measured these transition energy spectra by taking the difference of two photodiode outputs due to multiple beams of a single laser scanned over a range of frequencies and shone through a cell of Rb vapor. When the laser frequency was resonant with an atomic transition, photons of those frequencies were absorbed, leaving a dip in intensity of the beam measured at the photodiode. One of the two laser beams had …

Photoassociative Spectroscopy Of Ultracold Argon And Krypton Confined In A Magneto Optical Trap, Maha Khaled Omar

Physics Theses & Dissertations

Creating ultracold molecules has attracted considerable interest in the last decade. Once created, such molecules can be used for precision spectroscopy or to study chemical reactions at ultracold tem peratures. Several techniques have been developed to produce ultracold molecules; the most common is photoassociation where two ultracold atoms collide in the presence of light that induces a free-bound transition to an excited molecular state. Photoassociation can also be used to perform spectroscopy in order to map out the ro-vibrational levels of a molecular state. In this dissertaiotn, we report on our Photoasociative Spectroscopy (PAS) studies conducted separately in argon and …

Experimental Constraints On Exotic Spin-Dependent Interactions Using Specialized Materials, Rakshya Khatiwada

Open Access Dissertations

Various theories predict the possible existence of symmetry violating forces with mesoscopic range interactions from mm-m [1]. These forces can arise from the coupling of a spin 0 boson to spin 1/2 fermions through scalar (gs) and pseudoscalar (gp) couplings. We discuss two experiments that can investigate these interactions using nucleon rich, impressively low magnetic susceptibility (5-100 times lower than pure water) test masses and electron-spin rich, polarized test masses (spin density: 10^20 h/cm3 ). The first experiment looks for a P-odd, T-odd interaction potential proportional to (S.r) where S is the spin of one particle and r is the …

Catalysis Of Stark-Tuned Interactions Between Ultracold Rydberg Atoms, Aye Lu Win

Physics Theses & Dissertations

We present the study of the catalysis effect in the resonant energy transfer between ultracold ⁸⁵Rb Rydberg atoms. We have investigated the energy transfer process of 34p + 34p → 34s + 35s, and observed Stark-tuned Forster resonances. When additional Rydberg atoms of 34d state are included in the interaction, an increase in the population of 34s states atoms is observed. Although the 34d state atoms do not directly participate in the resonant energy transfer that produces 34s state atoms, they add an additional interaction channel 34p + 34 …

Rescattering Effects In Laser-Assisted Electron-Atom Bremsstrahlung, A. N. Zheltukhin, A. V. Flegel, M. V. Frolov, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

Rescattering effects in non-resonant spontaneous laser-assisted electron–atom bremsstrahlung (LABrS) are analyzed within the framework of time-dependent effective-range (TDER) theory. It is shown that high energy LABrS spectra exhibit rescattering plateau structures that are similar to those that are well-known in strong field laser-induced processes as well as those that have been predicted theoretically in laser-assisted collision processes. In the limit of a low-frequency laser field, an analytic description of LABrS is obtained from a rigorous quantum analysis of the exact TDER results for the LABrS amplitude. This amplitude is represented as a sum of factorized terms involving three factors, each …

Discrete Excitation Spectrum Of A Classical Harmonic Oscillator In Zero-Point Radiation, Wayne Cheng-Wei Huang, Herman Batelaan

Department of Physics and Astronomy: Faculty Publications

We report that upon excitation by a single pulse, a classical harmonic oscillator immersed in the classical electromagnetic zero-point radiation exhibits a discrete harmonic spectrum in agreement with that of its quantum counterpart. This result is interesting in view of the fact that the vacuum field is needed in the classical calculation to obtain the agreement.

Fission Fragment Tracking And Identification In The Neutron-Induced Fission Fragment Tracking Experiment’S Time Projection Chamber, Eric Song

Physics

The Neutron-Induced Fission Fragment Tracking Experiment (NIFFTE) built a novel Time Projection Chamber (TPC), the FissionTPC, for measuring neutron-induced fission cross-sections to unprecedented precision. We investigated data from a 2014 run (400010151) at the Los Alamos Neutron Science Center (LANSCE) with a double-sided U235/Pu239 target. Our particle identification studies will aid in the development of improved tracking algorithms.

Comment On “Universality Of Returning Electron Wave Packet In High-Order Harmonic Generation With Midinfrared Laser Pulses”, M. V. Frolov, N. L. Manakov, Wei-Hao Xiong, Liang-You Peng, J. Burgdörfer, Anthony F. Starace

Anthony F. Starace Publications

In conclusion, we have shown that when the same definition for the HHG yield is used [cf. Eq. (1)], the results of Ref. [1] give the same scaling law found earlier in Refs. [2–5] for wavelengths λ ≤ 2 μm. We note that this latter scaling law can be obtained analytically by using results of the model developed in Ref. [6] for the description of short-pulse HHG spectra. These analytic results as well as new numerical TDSE results for longer wavelengths, λ ≤ 4 μm, will be published elsewhere.

Enhancement Of Local Piezoresponse In Polymer Ferroelectrics Via Nanoscale Control Of Microstructure, Yoon-Young Choi, Pankaj Sharma, Charudatta Phatak, David J. Gosztola, Yunya Liu, Joonseok Lee, Byeongdu Lee, Jiangyu Li, Alexei Gruverman, Stephen Ducharme, Seungbum Hong

Stephen Ducharme Publications

Polymer ferroelectrics are flexible and lightweight electromechanical materials that are widely studied due to their potential application as sensors, actuators, and energy harvesters. However, one of the biggest challenges is their low piezoelectric coefficient. Here, we report a mechanical annealing effect based on local pressure induced by a nanoscale tip that enhances the local piezoresponse. This process can control the nanoscale material properties over a microscale area at room temperature. We attribute this improvement to the formation and growth of β-phase extended chain crystals via sliding diffusion and crystal alignment along the scan axis under high mechanical stress. We believe …

Simultaneous Analysis Of The Ballik-Ramsay And Phillips Systems Of C2 And Observation Of Forbidden Transitions Between Singlet And Triplet States, Wang Chen, Kentarou Kawaguchi, Peter F. Bernath, Jian Tang

Chemistry & Biochemistry Faculty Publications

6229 lines of the Ballik-Ramsay system (b₃Σ_g^--a₃Π_u) and the Phillips system (A¹Π_u-X¹Σ_g⁺) of C₂ up to v = 8 and J = 76, which were taken from the literature or assigned in the present work, were analyzed simultaneously by least-squares fitting with 82 Dunham-like molecular parameters and spin-orbit interaction constants between the b₃Σ_g^- and X¹Σ_g⁺ states with a standard deviation of 0.0037 cm^-1 for the whole data set. As a …

Theoretical Investigation Of Stabilities And Optical Properties Of Si12C12 Clusters, Xiaofeng F. Duan, Larry W. Burggraf

Faculty Publications

By sorting through hundreds of globally stable Si₁₂C₁₂ isomers using a potential surface search and using simulated annealing, we have identified low-energy structures. Unlike isomers knit together by Si–C bonds, the lowest energy isomers have segregated carbon and silicon regions that maximize stronger C–C bonding. Positing that charge separation between the carbon and silicon regions would produce interesting optical absorption in these cluster molecules, we used time-dependent density functional theory to compare the calculated optical properties of four isomers representing structural classes having different types of silicon and carbon segregation regions. Absorptions involving charge transfer between segregated …

Lifetime Measurement Of The Cesium 6p3/2 Level Using Ultrafast Pump-Probe Laser Pulses, B. M. Patterson, J. F. Sell, T. Ehrenreich, M. A. Gearba, G. M. Brooke, J. Scoville, R. J. Knize

Faculty Publications

Using the inherent timing stability of pulses from a mode-locked laser, we measure the cesium 6P_3/2 excited-state lifetime. An initial pump pulse excites cesium atoms in two counterpropagating atomic beams to the 6P_3/2 level. A subsequent synchronized probe pulse ionizes atoms that remain in the excited state and the photoions are collected and counted. By selecting pump pulses that vary in time with respect to the probe pulses, we obtain a sampling of the excited-state population in time, resulting in a lifetime value of 30.462(46) ns. The measurement uncertainty (0.15%) is slightly larger than our previous report of …

Charged Particle Dynamics In The Magnetic Field Of A Long Straight Current-Carrying Wire, M. Fatuzzo, A. Prentice, T. Toepker

Faculty Scholarship

The article discusses the concept behind motion of a charged particle in a non-uniform filed of a wire carrying current. Topics discussed include possible types of motion in a current carrying field, vector analysis of velocity and magnetic field of the particle and Coupled differential equations.

Compact Source Of Narrowband And Tunable X-Rays For Radiography, Sudeep Banerjee, Shouyuan Chen, Nathan D. Powers, Daniel Haden, Cheng Liu, Grigory V. Golovin, Jun Zhang, Baozhen Zhao, S. Clarke, Sara Pozzi, Jack Silano, H. Karwowski, Donald Umstadter

Donald Umstadter Publications

We discuss the development of a compact X-ray source based on inverse-Compton scattering with a laser-driven electron beam. This source produces a beam of high-energy X-rays in a narrow cone angle (5–10 mrad), at a rate of 108 photons-s_1. Tunable operation of the source over a large energy range, with energy spread of ~50%, has also been demonstrated. Photon energies >10 MeV have been obtained. The narrowband nature of the source is advantageous for radiography with low dose, low noise, and minimal shielding.

All-Laser-Driven Thomson X-Ray Sources, Donald Umstadter

Donald Umstadter Publications

We discuss the development of a new generation of accelerator-based hard X-ray sources driven exclusively by laser light. High-intensity laser pulses serve the dual roles: first, accelerating electrons by laser-driven plasma wakefields, and second, generating X-rays by inverse Compton scattering. Such all-laser-driven X-rays have recently been demonstrated to be energetic, tunable, relatively narrow in bandwidth, short pulsed and well collimated. Such characteristics, especially from a compact source, are highly advantageous for numerous advanced X-ray applications—in metrology, biomedicine, materials, ultrafast phenomena, radiology and fundamental physics.

Electrostatic Charge On Flying Hummingbirds And Its Potential Role In Pollination, Marc Badger, Victor Manuel Ortega-Jimenez, Lisa Von Ribenau, Ashley Smiley, Robert Dudley, Alexei Gruverman , Editor

Alexei Gruverman Publications

Electrostatic phenomena are known to enhance both wind- and insect-mediated pollination, but have not yet been described for nectar-feeding vertebrates. Here we demonstrate that wild Anna's Hummingbirds (Calypte anna) can carry positive charges up to 800 pC while in flight (mean ± s.d.: 66 ± 129 pC). Triboelectric charging obtained by rubbing an isolated hummingbird wing against various plant structures generated charges up to 700 pC. A metal hummingbird model charged to 400 pC induced bending of floral stamens in four plants (Nicotiana, Hemerocallis, Penstemon, and Aloe spp.), and also attracted falling Lycopodium spores at distances of < 2 mm. Electrostatic forces may therefore influence pollen transfer onto nectar-feeding birds.

Manipulating Topological States By Imprinting Non-Collinear Spin Textures, Robert Streubel, Luyang Han, Mi Young Im, Florian Kronast, Ulrich K. Rößler, Florin Radu, Radu Abrudan, Gungun Lin, Oliver G. Schmidt, Peter Fischer, Denys Makarov

Robert Streubel Papers

Topological magnetic states, such as chiral skyrmions, are of great scientific interest and show huge potential for novel spintronics applications, provided their topological charges can be fully controlled. So far skyrmionic textures have been observed in noncentrosymmetric crystalline materials with low symmetry and at low temperatures. We propose theoretically and demonstrate experimentally the design of spin textures with topological charge densities that can be tailored at ambient temperatures. Tuning the interlayer coupling in vertically stacked nanopatterned magnetic heterostructures, such as a model system of a Co/Pd multilayer coupled to Permalloy, the in-plane non-collinear spin texture of one layer can be …

Dr. Hetrick's Last Lecture, James Hetrick

Last Lecture

After finishing his Bachelor's degree in Physics from Case Western Reserve University, Dr. Hetrick spent 13 months at the South Pole Station in Antarctica where he studied cosmic rays, the solar wind, the auroras, and the earth's magnetosphere.

He received his Ph.D. from the University of Minnesota in theoretical particle physics and went on to postdoctoral research positions at ETH in Zürich, the University of Amsterdam, the University of Arizona, and Washington University in St. Louis, before coming to the University of the Pacific in 1997.

At Pacific, Professor Hetrick teaches a variety of classes, including courses like "Cosmology" and …

Multiferroic Tunnel Junctions And Ferroelectric Control Of Magnetic State At Interface, Y. W. Yin, M. Raju, W. J. Hu, John D. Burton, Y.-M. Kim, A. Y. Borisevich, S. J. Pennycook, S. M. Yang, T. W. Noh, Alexei Gruverman, X. G. Li, Z. D. Zhang, Evgeny Y. Tsymbal, Qi Li

Alexei Gruverman Publications

As semiconductor devices reach ever smaller dimensions, the challenge of power dissipation and quantum effect place a serious limit on the future device scaling. Recently, a multiferroic tunnel junction (MFTJ) with a ferroelectric barrier sandwiched between two ferromagnetic electrodes has drawn enormous interest due to its potential applications not only in multi-level data storage but also in electric field controlled spintronics and nanoferronics. Here, we present our investigations on four-level resistance states, giant tunneling electroresistance (TER) due to interfacial magnetoelectric coupling, and ferroelectric control of spin polarized tunneling in MFTJs. Coexistence of large tunneling magnetoresistance and TER has been observed …

Chirally-Sensitive Electron-Molecule Interactions, J. M. Dreiling, Timothy J. Gay

Timothy J. Gay Publications

All molecular forms of life have chemically-specific handedness. However, the origin of these asymmetries is not understood. A possible explanation was suggested by Vester and Ulbricht immediately following the discovery of parity violation in 1957: chiral beta radiation in cosmic rays may have preferentially destroyed one enantiomeric form of various biological precursors. In the experiments reported here, we observed chiral specificity in two electronmolecule interactions: quasi-elastic scattering and dissociative electron attachment. Using lowenergy longitudinally spin-polarized (chiral) electrons as substitutes for beta rays, we found that chiral bromocamphor molecules exhibited both a transmission and dissociative electron attachment rate that depended on …

Magnetic Soft X-Ray Tomography Of Magnetic Swiss Roll Architectures, Robert Streubel, F. Kronast, P. Fischer, O. G. Schmidt, D. Makarov

Robert Streubel Papers

A further increase in performance of state-of-the-art spin-electronics can be achieved by either miniaturizing its functional components or harnessing the third dimension. The first route, however, faces physical limitations as properties of nanostructures and their response to external stimuli can drastically change in reduced dimensions. An alternative way is to go from planar 2D structures to 3D architectures [1]. Such 3D functional elements can be obtained for example by rolling up initially planar strained thin films into Swiss roll like objects with multiple windings (Fig. 1a). A major advantage of this technology platform is the possibility to fabricate compact multifunctional …

Anomalous Nonlinear X-Ray Compton Scattering, Matthias Fuchs, Mariano Trigo, Jian Chen, Shambhu Ghimire, Sharon Shwartz, Michael Kozina, Mason Jiang, Thomas Henighan, Crystal Bray, Georges Ndabashimiye, Philip H. Bucksbaum, Yiping Feng, Sven Herrmann, Gabriella A. Carini, Jack Pines, Philip Hart, Christopher Kenney, Serge Guillet, Sébastien Boutet, Garth J. Williams, Marc Messerschmidt, M. Marvin Seibert, Stefan Moeller, Jerome B. Hastings, David A. Reis

Matthias Fuchs Publications

X-ray scattering is typically used as a weak linear atomic-scale probe of matter. At high intensities, such as produced at free-electron lasers, nonlinearities can become important, and the probe may no longer be considered weak. Here we report the observation of one of the most fundamental nonlinear X-ray–matter interactions: the concerted nonlinear Compton scattering of two identical hard X-ray photons producing a single higher-energy photon. The X-ray intensity reached 4 × 10²⁰ W cm⁻², corresponding to an electric field well above the atomic unit of strength and within almost four orders of magnitude of the quantum-electrodynamic critical …

Magnetic Force Microscopy Study Of Zr2co11-Based Nanocrystalline Materials: Effect Of Mo Addition, Lanping Yue, Yunlong Jin, Wenyong Zhang, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

The addition of Molybdenum was used to modify the nanostructure and enhance coercivity of rare-earth-free Zr₂Co₁₁-based nanocrystalline permanent magnets. The effect of Mo addition on magnetic domain structures of melt spun nanocrystalline Zr₁₆Co_84−xMo_x (𝑥 = 0, 0.5, 1, 1.5, and 2.0) ribbons has been investigated. It was found that magnetic properties and local domain structures are strongly influenced by Mo doping. The coercivity of the samples increases with the increase in Mo content (𝑥 ≤ 1.5). The maximum energy product (𝐵𝐻)_max increases with increasing 𝑥 from 0.5 MGOe for 𝑥 …