• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 657
  • 330
  • 126
  • 30
  • 11
  • 11
  • 11
  • 11
  • 11
  • 11
  • 2
  • 2
  • Tagged with
  • 1232
  • 1232
  • 872
  • 844
  • 264
  • 242
  • 221
  • 188
  • 163
  • 161
  • 125
  • 104
  • 101
  • 95
  • 95
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
131

Absolute differential and integral cross sections for charge transfer of state-selected keV oxygen ion with oxygen(2)

Merrill, Robert Louis January 1998 (has links)
Absolute differential and integral charge transfer cross sections have been measured for 0.5, 0.85, 1.5, 2.8, and 5.0 keV O$\sp+$ with O$\sb2$ at scattering angles between 0.01$\sp\circ$ and 3.50$\sp\circ$ in the laboratory frame. The dependence of these cross sections upon the electronic state of the O$\sp+$ ion was investigated. This study was performed using a filter cell technique to derive the cross sections for both the $\rm O\sp+(\sp4S)$ ground state ions and the $\rm O\sp+({\sp2D,\ \sp2P})$ metastable state ions. The charge transfer cross sections involving the $\rm O\sp+({\sp2D,\ \sp2P})$ ions are significantly larger than the corresponding cross sections for the ground state ions. Previously published cross section measurements are compared to the present results for the total integral charge transfer cross sections of state-selected keV O$\sp+$ with O$\sb2$.
132

Novel permanent-magnet Penning trap for studies of dipole-bound negative ions

Suess, Leonard Elmer January 2002 (has links)
Low-energy electron transfer between a Rydberg atom and a target molecule can result in formation of long-lived metastable negative ions. Here we describe a novel permanent-magnet Penning trap designed to examine the lifetime of such long lived metastable negative ions. With the help of ion trajectory calculations, the characteristics of the trap have been investigated and the most effective methods for ion injection have been established. Collisions with SF6, which has a high electron attachment rate, result in the formation of SF-*6 ions which are known to have a long intermediate lifetime. Comparisons between experimental SF-*6 trapping data and ion trajectory calculations are discussed that demonstrate the capabilities of the trap. Future experimental studies are also proposed.
133

422 nm laser

Simien, Clayton Earl January 2005 (has links)
A 422 nm laser was constructed for the purpose of studying a strontium ultra-cold neutral plasma. Since strontium ions have atomic lines in the visible, we can optically image the plasma via the 88 Sr+ 2S1/2 → 2 P1/2 transition using 422 nm light. We produce light at this wavelength by converting infrared light at 844 nm from a commercial semiconductor infrared diode laser via second-harmonic generation in an semi-monolithic linear enhancement cavity. This thesis will cover the experimental details pertaining to nonlinear optics, optical resonator design, and locking electronics used to create a 422 nm laser.
134

Saturation effects in photoassociation spectroscopy of strontium-86

Mickelson, Pascal Gerry January 2006 (has links)
This work describes intensity saturation of photoassociative transitions of 86Sr at the quantum mechanical unitarity limit. The saturation behavior, which results in a roll-over of the photoassociation rate for intensities greater than the saturation intensity, features interesting physics. Unlike other photoassociation spectroscopy (PAS) experiments, photoassociation occurs in a magneto-optical trap operating on the narrow dipole-forbidden transition at 689 nm. A laser red-detuned from the principal atomic transition at 461 nm by as much as 1300 GHz induces the photoassociation of ground state atoms to excited molecular states. Our previous studies [1] suggest that some of the PAS transitions for 86Sr are sensitive to the intensity of the laser. This work delves more deeply into these high intensity PAS effects, a subject that has not, to our knowledge, been studied experimentally for alkaline-earth atoms.
135

A narrow linewidth diode laser system for strontium laser cooling applications

Nagel, Sarah B. January 2004 (has links)
The diode laser system for laser cooling on the 1S 0 → 3P1 intercombination line of strontium discussed in this thesis allows us to cool and trap an atomic strontium sample to 15 muK. Samples in this temperature range are useful for the development of the next generation of atomic frequency standards, cold collision studies, and as a step towards quantum degeneracy. This laser system consists of a Littrow configuration external-cavity diode laser, which is frequency locked to a high finesse cavity. The cavity is subsequently locked to an absorption feature to produce a few mW of tunable, stabilized, single mode power at the target wavelength. We present the design and characterization of this system, including a linewidth measurement of 70 kHz, as well as preliminary results from cooling and trapping.
136

Dynamics of Rydberg electron transfer to acetonitrile: Velocity-dependent studies

Liu, Yi January 2005 (has links)
Collisions between atoms in high Rydberg states and polar targets can lead to the formation of dipole-bound negative ions. We examine the dynamics of CH3CN- ion production through electron transfer in K(np)/CH3CN collisions using velocity selected Rydberg atoms. The CH3CN- ion formation rate decreases markedly with decreasing Rydberg atom velocity, principally as a consequence of postattachment electrostatic interactions between the product ions. Implemented using Monte Carlo techniques, a curve-crossing model, which considers the effect of crossings between the diabetic potential curves for the covalent K(np)/CH3CN system and the K+/CH3CN - system, provides a clear explanation of several characteristics seen in electron transfer in K(np)/CH3CN collisions including: the n dependence in the CH3CN- ion production rate, the velocity dependence in the CH3CN- ion production rate, and the relatively small rate constant ∼0.5 - 1.0 x 10-8cm3 s-1 for production of long-lived CH3CN - ions.
137

Pulsed dye laser for excitation of strontium

Gupta, Priya January 2004 (has links)
This thesis describes the construction and characterization of a high energy, tunable, pulsed dye laser that is used to make ultracold strontium plasma. In order to make ultracold plasma, we cool and trap strontium atoms in a magneto-optical trap (MOT) and then photoionize them with the dye laser. The dye laser is pumped by high-energy 355nm pulses from a commercial Nd:YAG laser and it gives out 10ns pulses of 400--415nm light with up to 50mJ/pulse. We will discuss the lasers spectrum, wavelength calibration, output power and efficiency for photoionizing strontium.
138

Intelligent autonomous inductively coupled plasma instrumental operation

Webb, Douglas P. January 1996 (has links)
The development of a framework for the automated analysis of inductively couple plasma atomic emission spectroscopy is present. Some of the research that lead to current state of this framework is presented. A small expert system that uses information about the current sample to generate a line search strategy which minimizes the number of emission lines which need to be measured, and avoids spectral overlaps when possible. A program is presented that evaluates the minimum number of spectral windows required to perform elemental analysis by ICP-AES, given a certain spectral window width. A method with the potential for rapidly ascertaining the physical properties of the sample matrix is presented. This system has the potential to help reduce sample introduction related system failures. Finally, three optimization algorithms are compared in their ability to optimize ICP-AES performance, from this an optimization module was developed for inclusion in the automated analysis framework.
139

Collinear fast-beam laser spectroscopy at ISAC

Cocolios, Thomas Elias January 2005 (has links)
Collinear fast-beam laser spectroscopy is a method of studying atomic and ionic hyperfine structure where a particle beam and a laser beam are superposed along the same line. Such a facility exists at ISAC, TRIUMF, Vancouver, BC, and was designed especially for polarising radioactive beams of alkali metals. / In order to produce polarised fluorine for the use in NMR, the hyperfine structure of the 3s 4P 5/2 and 3p 4D 7/2 states has to be known. The hyperfine coefficients for those two levels are measured for the first time to be A = 2645.6(6) MHz and A = 1565.6(4)MHz respectively. The 3p 4D5/2 state is also studied to measure the metastable atom fraction and its hyperfine constant is measured to be A = 1148(5)MHz. / A study of lanthanum ions is also carried out. Spectra for the 6 s2 1S0 to 5 d6p Do13 transition are measured with stable 139La to evaluate the sensitivity of the equipment and with radioactive 139La for preliminary commissioning of the isotope shift study.
140

Quantum Trajectories of a Superconducting Qubit

Weber, Steven Joseph 27 March 2015 (has links)
<p> In quantum mechanics, the process of measurement is intrinsically probabilistic. As a result, continuously monitoring a quantum system will randomly perturb its natural unitary evolution. An accurate measurement record documents this stochastic evolution and can be used to reconstruct the quantum trajectory of the system state in a single experimental iteration. We use weak measurements to track the individual quantum trajectories of a superconducting qubit that evolves under the competing influences of continuous weak measurement and Rabi drive. We analyze large ensembles of such trajectories to examine their characteristics and determine their statistical properties. For example, by considering only the subset of trajectories that evolve between any chosen initial and final states, we can deduce the most probable path through quantum state space. Our investigation reveals the rich interplay between measurement dynamics, typically associated with wavefunction collapse, and unitary evolution. Our results provide insight into the dynamics of open quantum systems and may enable new methods of quantum state tomography, quantum state steering through measurement, and active quantum control.</p>

Page generated in 0.0613 seconds