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Full-Text Articles in Physics

Helmholtz Spacing Of Thin Rectangular Magnetic Field Coils, Karl J. Ahrendsen, Sarah Reyes, Timothy J. Gay Nov 2020

Helmholtz Spacing Of Thin Rectangular Magnetic Field Coils, Karl J. Ahrendsen, Sarah Reyes, Timothy J. Gay

Timothy J. Gay Publications

In this Note, we discuss the Helmholtz spacing for a pair of thin rectangular coils of arbitrary aspect ratio and consider how best to use such coils to compensate for Earth’s magnetic field along the coils’ Cartesian symmetry axes. Such coils are frequently used in conjunction with charged-particle beam machines. The Helmholtz spacing varies non-monotonically between that for square coils and that for four optimally spaced infinite wires. We consider other coil spacings that extend the length over which the field varies by less than some tolerance along the Cartesian symmetry axes. The calculations also provide a convenient means ...


The Paradox Of The Tight Spiral Pass In American Football: A Simple Resolution, Richard H. Price, William C. Moss, Timothy J. Gay Jan 2020

The Paradox Of The Tight Spiral Pass In American Football: A Simple Resolution, Richard H. Price, William C. Moss, Timothy J. Gay

Timothy J. Gay Publications

An American football is a rotationally symmetric object, which, when well-thrown, spins rapidly around its symmetry axis. In the absence of aerodynamic effects, the football would be a torque-free gyroscope and the symmetry/spin axis would remain pointing in a fixed direction in space as the football moved on its parabolic path. When a pass is well-thrown through the atmosphere, however, the symmetry axis remains—at least approximately—tangent to the path of motion. The rotation of the symmetry axis must be due to aerodynamic torque; yet, that torque, at first glance, would seem to have precisely the opposite effect ...


Femtosecond-Laser-Induced Spin-Polarized Electron Emission From A Gaas Tip, Evan M. Brunkow, Eric R. Jones, Herman Batelaan, Timothy J. Gay Feb 2019

Femtosecond-Laser-Induced Spin-Polarized Electron Emission From A Gaas Tip, Evan M. Brunkow, Eric R. Jones, Herman Batelaan, Timothy J. Gay

Timothy J. Gay Publications

It is shown that focusing circularly polarized 800nm light pulses of duration 100 fs on the tips of p-GaAs crystalline shards having no negative electron affinity (NEA) activation results in electron emission that is both fast and spin-polarized. The 400 fs duration of the emission process was determined by pump/probe measurements. The three samples we investigated produced electron polarizations of 13.1(0.9)%, 13.3(0.7)%, and 10.4(0.2)%. Emission currents ranged between 50 pA and 3 nA with a sample bias of –100 V and an average laser power of 100 mW. The electron ...


Spin- And Angle-Resolved Photoemission Studies Of The Electronic Structure Of Si(110)“16×2” Surfaces, N. K. Lewis, Y. Lassailly, L. Martinelli, I. Vobornik, J. Fujii, C. Bigi, Evan M. Brunkow, Nathan B. Clayburn, Timothy J. Gay, W. R. Flavell, E. A. Seddon Jan 2019

Spin- And Angle-Resolved Photoemission Studies Of The Electronic Structure Of Si(110)“16×2” Surfaces, N. K. Lewis, Y. Lassailly, L. Martinelli, I. Vobornik, J. Fujii, C. Bigi, Evan M. Brunkow, Nathan B. Clayburn, Timothy J. Gay, W. R. Flavell, E. A. Seddon

Timothy J. Gay Publications

The electronic structure of Si(110)“16×2” double-domain, single-domain, and 1×1 surfaces have been investigated using spin- and angle-resolved photoemission at sample temperatures of 77K and 300K. Angleresolved photoemission was conducted using horizontally and vertically polarized 60 eV and 80 eV photons. Band-dispersion maps revealed four surface states (S1 to S4) which were assigned to silicon dangling bonds on the basis of measured binding energies and photoemission intensity changes between horizontal and vertical light polarizations. Three surface states (S1, S2, and S4), observed in the Si(110)“16×2” reconstruction, were assigned to ...


Spin-Polarized Electron Transmission Through Chiral Halocamphor Molecules, J. M. Dreiling, F. W. Lewis, Timothy J. Gay Jan 2018

Spin-Polarized Electron Transmission Through Chiral Halocamphor Molecules, J. M. Dreiling, F. W. Lewis, Timothy J. Gay

Timothy J. Gay Publications

We have measured electron-circularly-dichroic asymmetries when longitudinally-polarized (chiral) electrons are scattered quasi-elastically by chiral halocamphor molecules: 3-bromocamphor (C10H15BrO), 3-iodocamphor (C10H15IO), and 10-iodocamphor. The proposed dynamic origins of these asymmetries are considered in terms of three classical models related to Mott scattering, target electron helicity density, and spin-other-orbit interactions. The asymmetries observed for 3-bromocamphor and 3-iodocamphor scale roughly as Z2, where Z is the nuclear charge of the heaviest atom in the target molecule, but the scaling is violated by 10- iodocamphor, which has a smaller asymmetry than that for 3-iodocamphor. This ...


Alignment Of The (3D104S5S)3S1 State Of Zn Excited By Polarized Electron Impact, Nathan B. Clayburn, Timothy J. Gay Sep 2017

Alignment Of The (3D104S5S)3S1 State Of Zn Excited By Polarized Electron Impact, Nathan B. Clayburn, Timothy J. Gay

Timothy J. Gay Publications

We measure the integrated Stokes parameters of light from Zn (4s4p)43P0,1-(4s5s)53S1 transitions excited by a transversely polarized electron impact at energies between 7.0 and 8.5 eV. Our results for the electron-polarization-normalized linear polarization Stokes parameter P2, between incident electron energies 7.0 and 7.4 eV, are consistent with zero, as required by basic angular-momentum coupling considerations and by recent theoretical calculations. They are in qualitative disagreement with previous experimental results for the P2 parameter.


Measurement Of The Integrated Stokes Parameters Of Zn 468 Nm Fluorescence Excited By Polarized-Electron Impact, Nathan B. Clayburn, Timothy J. Gay Jan 2017

Measurement Of The Integrated Stokes Parameters Of Zn 468 Nm Fluorescence Excited By Polarized-Electron Impact, Nathan B. Clayburn, Timothy J. Gay

Timothy J. Gay Publications

The integrated Stokes parameters P1, P2, and P3 of Zn (43P0,1 – 53S1) fluorescence resulting from transversely-spin-polarized electron impact excitation of the Zn (4s5s)53S1 state have been measured. This work was motivated by similar studies reported several years ago, in which non-zero values of the integrated Stokes parameter P2 between the threshold for the (4s5s)53S1 excitation and the first cascading (4s5p)53PJ threshold were measured. We observe optical excitation functions in agreement with previous experimental and theoretical results, but ...


Domain Formation Mechanism Of The Si(110) “16 × 2” Reconstruction, N. K. Lewis, Nathan B. Clayburn, Evan M. Brunkow, Timothy J. Gay, Y. Lassailly, J. Fujii, I. Vobornik, W. R. Flavell, E. A. Seddon Jan 2017

Domain Formation Mechanism Of The Si(110) “16 × 2” Reconstruction, N. K. Lewis, Nathan B. Clayburn, Evan M. Brunkow, Timothy J. Gay, Y. Lassailly, J. Fujii, I. Vobornik, W. R. Flavell, E. A. Seddon

Timothy J. Gay Publications

The main factor that determines which of the two domains forms upon reconstruction of the Si(110) “16 × 2” surface has been investigated. Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) images showed that the domain orientation was independent of the heating current direction used to induce the Si(110) “16 × 2” reconstruction. Reciprocal-space lattice models of the reconstruction allowed for the correct identification of domain orientations in the LEED images, and they confirmed that the reconstruction is two dimensionally chiral. It is proposed that the domain orientation upon surface reconstruction is determined by the direction of monatomic steps ...


A Cylindrically Symmetric “Micro-Mott” Electron Polarimeter, Nathan B. Clayburn, Evan M. Brunkow, S. J. Burtwistle, George H. Rutherford, Timothy J. Gay May 2016

A Cylindrically Symmetric “Micro-Mott” Electron Polarimeter, Nathan B. Clayburn, Evan M. Brunkow, S. J. Burtwistle, George H. Rutherford, Timothy J. Gay

Timothy J. Gay Publications

A small, novel, cylindrically symmetric Mott electron polarimeter is described. The effective Sherman function, Seff , or analyzing power, for 20 kV Au target bias with a 1.3 keV energy loss window is 0.16 ± 0.01, where uncertainty in the measurement is due primarily to uncertainty in the incident electron polarization. For an energy loss window of 0.5 keV, Seff reaches its maximum value of 0.24 ± 0.02. The device’s maximum efficiency, I/Io, defined as the detected count rate divided by the incident particle rate, is 3.7 ± 0.2 ...


Method For Monitoring Gaas Photocathode Heat Cleaning Temperature, Nathan B. Clayburn, Kenneth Wayne Trantham, M. Dunn, Timothy J. Gay Jan 2016

Method For Monitoring Gaas Photocathode Heat Cleaning Temperature, Nathan B. Clayburn, Kenneth Wayne Trantham, M. Dunn, Timothy J. Gay

Timothy J. Gay Publications

Before a GaAs photocathode can be activated to achieve a negative electron affinity condition, the GaAs crystal must be cleaned. This is most commonly done by ohmic, radiative, or electron bombardment heating. We report a new technique to monitor the temperature of heated GaAs photocathodes by observation with a camera. The method is robust and yields the same temperatures for different GaAs samples heated using different methods in different mounting configurations.


Anomalously Large Chiral Sensitivity In The Dissociative Electron Attachment Of 10-Iodocamphor, J. M. Dreiling, F. W. Lewis, J. D. Mills, Timothy J. Gay Jan 2016

Anomalously Large Chiral Sensitivity In The Dissociative Electron Attachment Of 10-Iodocamphor, J. M. Dreiling, F. W. Lewis, J. D. Mills, Timothy J. Gay

Timothy J. Gay Publications

We have studied dissociative electron attachment (DEA) between low energy (≤ 0.6 eV) longitudinally polarized electrons and gas-phase chiral targets of 3-bromocamphor (C10H15BrO), 3-iodocamphor (C10H15IO), and 10-iodocamphor. The DEA rate depends on the sign of the incident electron helicity for a given target handedness, and it varies with both the atomic number (Z) and location of the heaviest atom in the molecule. While simple dynamic mechanisms can account for the asymmetry dependence on Z, they fail to explain the large asymmetry variation with the heavy atom location.


Chirally-Sensitive Electron-Molecule Interactions, J. M. Dreiling, Timothy J. Gay Jan 2015

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 ...


Chirally Sensitive Electron-Induced Molecular Breakup And The Vester-Ulbricht Hypothesis, J. M. Dreiling, Timothy J. Gay Jan 2014

Chirally Sensitive Electron-Induced Molecular Breakup And The Vester-Ulbricht Hypothesis, J. M. Dreiling, Timothy J. Gay

Timothy J. Gay Publications

We have studied dissociative electron attachment in sub-eV collisions between longitudinally polarized electrons and chiral bromocamphor molecules. For a given target enantiomer, the dissociative Br anion production depends on the helicity of the incident electrons, with an asymmetry that depends on the electron energy and is of order 3 × 10−4. The existence of chiral sensitivity in a well-defined molecular breakup reaction demonstrates the viability of the Vester-Ulbrict hypothesis, namely, that the longitudinal polarization of cosmic beta radiation was responsible for the origins of biological homochirality.


Search For Spin-Polarized Photoemission From Gaas Using Light With Orbital Angular Momentum, Nathan B. Clayburn, J. L. Mccarter, J. M. Dreiling, M. Poelker, D. M. Ryan, Timothy J. Gay Jan 2013

Search For Spin-Polarized Photoemission From Gaas Using Light With Orbital Angular Momentum, Nathan B. Clayburn, J. L. Mccarter, J. M. Dreiling, M. Poelker, D. M. Ryan, Timothy J. Gay

Timothy J. Gay Publications

Laser light with photon energy near the band gap of GaAs and in Laguerre-Gaussian modes with different amounts of orbital angular momentum was used to produce photoemission from unstrained GaAs. The degree of electron spin polarization was measured using a micro-Mott polarimeter and found to be consistent with zero with an upper limit of ∼3% for light with up to ±5h of orbital angular momentum. In contrast, the degree of spin polarization of 32.3 ± 1.4% using circularly polarized laser light at the as the same wavelength, which is typical for bulk GaAs photocathodes.


Compact Inline Optical Electron Polarimeter, Munir Pirbhai, D. M. Ryan, G. Richards, Timothy J. Gay Jan 2013

Compact Inline Optical Electron Polarimeter, Munir Pirbhai, D. M. Ryan, G. Richards, Timothy J. Gay

Timothy J. Gay Publications

A compact optical electron polarimeter using a helium target is described. It offers a maximum fluorescence detection efficiency of ∼20 Hz/nA, which is an order of magnitude higher than that of earlier designs. With an argon target, this device is expected to have a polarimetric figure-of-merit of 270 Hz/nA. By relying on a magnetic field to guide a longitudinally spin-polarized electron beam, the present instrument employs fewer electrodes. It also uses a commercially available integrated photon counting module. These features allow it to occupy a smaller volume and make it easier to operate.


Optically Pumped Spin-Exchange Polarized-Electron Source, Munir Pirbhai, J. Knepper, E. T. Litaker, D. Tupa, Timothy J. Gay Jan 2013

Optically Pumped Spin-Exchange Polarized-Electron Source, Munir Pirbhai, J. Knepper, E. T. Litaker, D. Tupa, Timothy J. Gay

Timothy J. Gay Publications

We describe the operation of a prototype polarized-electron source. Rubidium vapor, contained in a cell, is optically pumped in the presence of a buffer gas. Unpolarized electrons from a tungsten filament are injected into the cell and extracted after undergoing spin exchange with the Rb atoms. We compare the performance of the source when different buffer gases are used. We measure a decrease in electron polarization as their injection energy increases, but find an unexpected regime at higher injection energies yielding increased electron polarization accompanied by a 40-fold increase in current, suggesting the production of slow secondary electrons in the ...


Two Novel Approaches For Electron Beam Polarization From Unstrained Gaas, James L. Mccarter, Nathan B. Clayburn, J. M. Dreiling, Timothy J. Gay, Dominic M. Ryan, John Hansknecht, Matt Poelker, Andrei Afanasev, Ara Kechiantz Jan 2013

Two Novel Approaches For Electron Beam Polarization From Unstrained Gaas, James L. Mccarter, Nathan B. Clayburn, J. M. Dreiling, Timothy J. Gay, Dominic M. Ryan, John Hansknecht, Matt Poelker, Andrei Afanasev, Ara Kechiantz

Timothy J. Gay Publications

Two novel approaches to producing highly-polarized electron beams from unstrained GaAs were tested using a micro-Mott polarimeter. Based on a suggestion by Nakanishi [1]], twophoton photoemission with 1560 nm light was used with photocathodes of varying thickness: 625m, 0.32m, and 0.18m. For each of these photocathodes, the degree of spin polarization of the photoemitted beam was less than 50%. Polarization via two-photon absorption was highest from the thinnest photocathode sample and close to that obtained from one-photon absorption (using 778 nm light), with values 40.3±1.0% and 42.6±1.0%, respectively. The ...


Threshold Alignment Reversal And Circularly Polarized Fluorescence In Rotationally Resolved H2, Jack W. Maseberg, Klaus Bartschat, Timothy J. Gay Jan 2013

Threshold Alignment Reversal And Circularly Polarized Fluorescence In Rotationally Resolved H2, Jack W. Maseberg, Klaus Bartschat, Timothy J. Gay

Timothy J. Gay Publications

Using H2 and D2 targets, we have measured the polarization of Fulcher-band fluorescence resulting from spin-polarized electron-impact excitation of vibrationally and rotationally resolved d 3Πu→ a 3g+ transitions for incident electron energies from 14.3 to 28.5 eV. Near threshold, the linear polarization P1 descends from positive values through zero to negative values, indicating a dynamic production of MN = 0 states. The circular polarization P3 is measured to be nonzero, indicating the orientation of rotationally resolved molecular states. For Q-branch transitions, P3 is consistent with theory based on Hund ...


Orientation Of Doubly Excited States In N2, John E. Furst, Timothy J. Gay, Joshua Machacek, David Kilkoyne, Kenneth W. Mclaughlin Jan 2012

Orientation Of Doubly Excited States In N2, John E. Furst, Timothy J. Gay, Joshua Machacek, David Kilkoyne, Kenneth W. Mclaughlin

Timothy J. Gay Publications

We have measured the total fluorescent intensity and circular polarization of light emitted in 3p 4Po → 3s4P transitions of excited neutral nitrogen atoms created by the photofragmentation of the N2 molecule with circularly polarized light having energies between 21 and 26 eV. The intensity measurements show the effect of predissociation of the N2 Rydberg series R(C) 1Σ+u states by non-Rydberg doubly excited resonances (NRDERs), while nonzero values of circular polarization allow us to unambiguously identify the presence of a directly excited NRDER with 1Πu symmetry in this ...


Transverse Measurements Of Polarization In Optically Pumped Rb Vapor Cells, J. M. Dreiling, E. B. Norrgard, D. Tupa, Timothy J. Gay Jan 2012

Transverse Measurements Of Polarization In Optically Pumped Rb Vapor Cells, J. M. Dreiling, E. B. Norrgard, D. Tupa, Timothy J. Gay

Timothy J. Gay Publications

We have developed a simple heuristic method for determining the polarization of an optically pumped alkalimetal vapor. A linearly polarized probe beam traverses a vapor cell perpendicular to the pump-beam propagation direction, and the transmitted beam intensity is monitored for orthogonal linear polarizations. As the probe beam is scanned in frequency across the D1 transition, its linear-polarization-dependent transmission can be used as a measure of the atomic orientation of the vapor. We analyze these transmission differences and their dependence on the alkali-metal number density in the vapor.


Detecting An Extended Light Source Through A Lens, E. T. Litaker, J. R. Machacek, Timothy J. Gay Jan 2011

Detecting An Extended Light Source Through A Lens, E. T. Litaker, J. R. Machacek, Timothy J. Gay

Timothy J. Gay Publications

We present a Monte Carlo simulation of a cylindrical luminescent volume and a typical lens–detector system. The results of this simulation yield a graphically simple picture of the regions within the cylindrical volume from which this system detects light. Because the cylindrical volume permits large angles of incidence, we use a modification of the thin-lens approximation for ray tracing. We compare simulation results with concepts from imaging optics, and comment on implications for experimental design.


Production Of Excited Atomic Hydrogen And Deuterium From H2, Hd And D2 Photodissociation, J R. Machacek, V M. Andrianarijaona, J. E. Furst, A L D Kilcoyne, A L Landers, E T Litaker, K W Mclaughlin, Timothy J. Gay Jan 2011

Production Of Excited Atomic Hydrogen And Deuterium From H2, Hd And D2 Photodissociation, J R. Machacek, V M. Andrianarijaona, J. E. Furst, A L D Kilcoyne, A L Landers, E T Litaker, K W Mclaughlin, Timothy J. Gay

Timothy J. Gay Publications

We have measured the production of Lyman α and Balmer α fluorescence from atomic H and D for the photodissociation of H2, HD and D2 by linearly-polarized photons with energies between 22 and 64 eV. We discuss systematic uncertainties associated with our data, and compare our results with previous experimental results and ab initio calculations of the dissociation process. We comment on the discrepancies.


Measurement Of Electron Beam Polarization From Unstrained Bulk Gaas Via Two Photon Photoemission, J L Mccarter, Timothy J. Gay, J Hansknecht, M Poelker, M L Stutzman Jan 2011

Measurement Of Electron Beam Polarization From Unstrained Bulk Gaas Via Two Photon Photoemission, J L Mccarter, Timothy J. Gay, J Hansknecht, M Poelker, M L Stutzman

Timothy J. Gay Publications

This paper describes measurements of the beam polarization and quantum efficiency for photo-emission using two-photon excitation from unstrained bulk GaAs illuminated with pulsed, high intensity 1560nm laser light. Quantum efficiency is linearly proportional to 1560nm peak laser intensity, which was varied in three independent ways, indicating that the emitted electrons are promoted from the valence to the conduction band via two-photon absorption. Beam polarization was measured using a microMott polarimeter, with a value of 16.8(4)% polarization at 1560nm, which is roughly half the measured value of 33.4(8)% using 778 nm light.


A Low-Voltage Retarding-Field Mott Polarimeter For Photocathode Characterization, J.L. Mccarter, M.L. Stutzman, K.W. Trantham, Timothy G. Anderson, A.M. Cook, Timothy J. Gay Jan 2010

A Low-Voltage Retarding-Field Mott Polarimeter For Photocathode Characterization, J.L. Mccarter, M.L. Stutzman, K.W. Trantham, Timothy G. Anderson, A.M. Cook, Timothy J. Gay

Timothy J. Gay Publications

Nuclear physics experiments at Thomas Jefferson National Accelerator Facility’s CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and operates from 5 to 30 kV. The effective Sherman function for this device has been calibrated by comparison with the CEBAF 5 MeV Mott polarimeter. For elastic scattering from a thick gold target at 20 keV, the effective Sherman function is 0.201(5). Its maximum efficiency at 20 ...


Electron-Spin-Reversal Phenomenon In Optically Pumped Rubidium, E. B. Norrgard, D. Tupa, J. M. Dreiling, Timothy J. Gay Jan 2010

Electron-Spin-Reversal Phenomenon In Optically Pumped Rubidium, E. B. Norrgard, D. Tupa, J. M. Dreiling, Timothy J. Gay

Timothy J. Gay Publications

We have studied the optical pumping of mixtures of Rb vapor and N2 buffer gas by laser light tuned to the D1 transition having a spectral width of ∼500 MHz. The Rb densities are of the order of 1013 cm−3, while the buffer-gas pressures range from 0.1 to 10 torr. As the frequency of the right-hand circularly polarized laser is varied across the D1 absorption profile, the electron spin polarization of the Rb is found to take on negative values for small negative values of pump detuning from the absorption profile center. This occurs for ...


Alignment And Orientation Of Diatomic Molecules Induced By Polarized Electron Impact, Jack W. Maseberg, Timothy J. Gay Jan 2010

Alignment And Orientation Of Diatomic Molecules Induced By Polarized Electron Impact, Jack W. Maseberg, Timothy J. Gay

Timothy J. Gay Publications

We report measurements of linear and circular fluorescence polarizations for molecular transitions in H2, D2, and N2 induced by spin-polarized electron impact. Circular polarizations resulting from some Fulcher-α transitions in H2 and D2 are found to be significant, while the null results from nitrogen’s second positive system are consistent with an earlier measurement by the Münster group. We compare this nitrogen data to that from our previous study of nitrogen’s first negative system. Emphasis is placed on understanding the mechanisms that cause the values of circular polarization from N2 to be relatively ...


Spin Torque On Molecular Rotation Induced By Polarized Electrons, J. W. Maseberg, Timothy J. Gay Jan 2009

Spin Torque On Molecular Rotation Induced By Polarized Electrons, J. W. Maseberg, Timothy J. Gay

Timothy J. Gay Publications

We have measured the linear and circular polarization of 391.4 nm N2+ B 2Σu+(υ’=0) → X2Σg+n=0) P-branch fluorescence produced by spin-polarized electron impact excitation of N2 X1 Σg+(υ=0) ground states. The resulting nonzero values of the circular polarization indicate that spin-rotation coupling, in conjunction with electron exchange excitation, acts to produce oriented rotational angular momenta in the excited molecular state prior to decay.


Use Of Partial-Wave Decomposition To Identify Resonant Interference Effects In The Photoionization–Excitation Of Argon, Timothy J. Gay, Chris H. Greene, J. R. Machacek, K. W. Mclaughlin, H. W. Van Der Hart, Orhan Yenen, Duane H. Jaecks Jan 2009

Use Of Partial-Wave Decomposition To Identify Resonant Interference Effects In The Photoionization–Excitation Of Argon, Timothy J. Gay, Chris H. Greene, J. R. Machacek, K. W. Mclaughlin, H. W. Van Der Hart, Orhan Yenen, Duane H. Jaecks

Timothy J. Gay Publications

We have studied simultaneous photoionization and excitation of Ar in the range of incident photon energies between 36.00 and 36.36 eV, where the resonant production of doubly excited neutral Ar states imbedded in the ionization continuum is dominant. By measuring the relative Stokes parameters of the fluorescence from residual Ar+∗ (3p4 [3P] 4p) ions (2P1/2, 465.8 nm transition; 2P3/2, 476.5 nm; 2D3/2, 472.7 nm; 2D5/2, 488.0 nm; 4P5/2, 480.6 nm; 4D5/2, 514.5 ...


Active Feedback Scheme For Minimization Of Helicity-Dependent Instrumental Asymmetries, M. I. Fabrikant, K. W. Trantham, V. M. Andrianarijaona, Timothy J. Gay May 2008

Active Feedback Scheme For Minimization Of Helicity-Dependent Instrumental Asymmetries, M. I. Fabrikant, K. W. Trantham, V. M. Andrianarijaona, Timothy J. Gay

Timothy J. Gay Publications

A method for the active feedback reduction of optical instrumental intensity asymmetries is presented. It is based on the fast chopping of two spatially separated beams of light with orthogonal linear polarizations that are recombined and passed through a quarter-wave plate to yield a single beam with rapidly flipping helicity. Active electro-optic feedback has been successfully employed to maintain this asymmetry below 10−5.


Radiation Trapping In Rubidium Optical Pumping At Low Buffer-Gas Pressures, Mark A. Rosenberry, J. P. Reyes, D. Tupa, Timothy J. Gay Feb 2007

Radiation Trapping In Rubidium Optical Pumping At Low Buffer-Gas Pressures, Mark A. Rosenberry, J. P. Reyes, D. Tupa, Timothy J. Gay

Timothy J. Gay Publications

We have made a systematic study of rubidium optical pumping in a simple cylindrical cell geometry with a high-power 10 W diode laser array, low magnetic fields, and buffer-gas pressures of less than 50 torr. We have determined rubidium polarizations experimentally for H2, N2, He, and Ar buffer gases, with Rb number densities from 1012 to 1013 cm-3. Comparison to a relatively simple optical pumping model allows us to extract useful information about radiation trapping and quenching effects.