Atomic, Molecular and Optical Physics Commons^™

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 …

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 …

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 …

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.

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 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 …

Construction And Optimization Of A Tapered Amplifier System For Applications In Ultra-Cold Plasma Research, Ryan Cole

Honors Theses

The number density of cold atoms confined in a magneto-optical trap (MOT) is critically dependent on the intensity of the lasers used to cool the sample. To generate large optical powers while retaining the practicality of homemade external cavity diode lasers (ECDLs), a tapered amplifier (TA) system was designed and constructed to amplify the output of an existing 780 nm, continuous-wave ECDL. The amplifier’s performance is discussed in terms of its gain and power output. Under standard operating conditions, optical amplification of 12 dB is achieved, with a maximum power output of 0.75 W. The completed amplifier is installed into …

Effect Of Strain On Ferroelectric Field Effect In Strongly Correlated Oxide Sm0.5Nd0.5Nio3, L. Zhang, X. G. Chen, H. J. Gardner, M. A. Koten, J. E. Shield, X. Hong

Xia Hong Publications

We report the effect of epitaxial strain on the magnitude and retention of the ferroelectric field effect in high quality PbZr_0.3Ti_0.7O₃ (PZT)/3.8-4.3 nm Sm_0.5Nd_0.5NiO₃ (SNNO) heterostructures grown on (001) LaAlO₃ (LAO) and SrTiO₃ (STO) substrates. For SNNO on LAO, which exhibits a first-order metal-insulator transition (MIT), switching the polarization of PZT induces a 10 K shift in the transition temperature T_MI, with a maximum resistance change between the on and off states of Δ��/��_on ~75%. In sharp contrast, only up to 5% resistance change has …

Magnetic Chiral Spin Textures By Imprinting, Robert Streubel, F. Kronast, U. Rössler, O. G. Schmidt, P. Fischer, D. Makarov

Robert Streubel Papers

The unique properties of non-trivial topological states, e.g. magnetic skyrmions [1] may path the way towards novel spintronic devices [2]. However, these spin textures have only been observed in special classes of materials possessing non-centrosymmetric crystal structure [1,3-6] and at low temperatures, which limits their application potential. We offer an alternate route to design synthetic magnetic heterostructures that resemble swirls, vortices or skyrmions with distinct topological charge densities at room temperature. By vertically stacking two magnetic nanopatterns with in-and out-of-plane magnetization and tailoring the interlayer exchange coupling, non-collinear spin textures with tunable topological charge can be imprinted (Fig. 1a).

Characterizing Double And Triple Laser Beam Interference Patterns In The Context Of Trapping Atoms For Quantum Computing, Ian E. Powell

Physics

We propose two optical neutral atom traps for quantum computing involving the intersection of two or three laser beams. We simulate both the intensity and the potential energy of the interference pattern. From these simulations we create animations of how the potential energy and intensity change with varying angles of separation between the laser beams in the system. We parameterize lines through our interference pattern and fit simple harmonic oscillator potential energies to the potential energy wells calculated to characterize our interference pattern’s atom trapping capabilities. Finally, we investigate a possible quantum entanglement routine by observing how the geometry of …