The Experts below are selected from a list of 46431 Experts worldwide ranked by ideXlab platform

Dmitry Budker - One of the best experts on this subject based on the ideXlab platform.

  • raman and nuclear magnetic resonance investigation of alkali Metal Vapor interaction with alkene based anti relaxation coating
    2016
    Co-Authors: Yu O Tretiak, Dmitry Budker, John W Blanchard, Pavel K Olshin, S N Smirnov, Misha Balabas
    Abstract:

    The use of anti-relaxation coatings in alkali Vapor cells yields substantial performance improvements compared to a bare glass surface by reducing the probability of spin relaxation in wall collisions by several orders of magnitude. Some of the most effective anti-relaxation coating materials are alpha-olefins, which (as in the case of more traditional paraffin coatings) must undergo a curing period after cell manufacturing in order to achieve the desired behavior. Until now, however, it has been unclear what physicochemical processes occur during cell curing, and how they may affect relevant cell properties. We present the results of nondestructive Raman-spectroscopy and magnetic-resonance investigations of the influence of alkali Metal Vapor (Cs or K) on an alpha-olefin, 1-nonadecene coating the inner surface of a glass cell. It was found that during the curing process, the alkali Metal catalyzes migration of the carbon-carbon double bond, yielding a mixture of cis- and trans-2-nonadecene.

  • polarized alkali Metal Vapor with minute long transverse spin relaxation time
    2010
    Co-Authors: Misha Balabas, Todor Karaulanov, M P Ledbetter, Dmitry Budker
    Abstract:

    We demonstrate lifetimes of Zeeman populations and coherences in excess of 60 sec in alkali-Metal Vapor cells with inner walls coated with an alkene material. This represents 2 orders of magnitude improvement over the best paraffin coatings. We explore the temperature dependence of cells coated with this material and investigate spin-exchange relaxation-free magnetometry in a room-temperature environment, a regime previously inaccessible with conventional coating materials.

  • magnetometry with millimeter scale antirelaxation coated alkali Metal Vapor cells
    2006
    Co-Authors: Misha Balabas, Dmitry Budker, John Kitching, Peter D D Schwindt, J E Stalnaker
    Abstract:

    Dynamic nonlinear magneto-optical-rotation signals with frequency- and amplitude-modulated laser light have been observed and investigated with a spherical glass cell of 3 mm diameter containing Cs Metal with inner walls coated with paraffin. Intrinsic Zeeman relaxation rates of γ/(2π)≈20 Hz and lower have been observed. Favorable prospects of using millimeter-scale coated cells in portable magnetometers and secondary frequency references are discussed.

Misha Balabas - One of the best experts on this subject based on the ideXlab platform.

  • raman and nuclear magnetic resonance investigation of alkali Metal Vapor interaction with alkene based anti relaxation coating
    2016
    Co-Authors: Yu O Tretiak, Dmitry Budker, John W Blanchard, Pavel K Olshin, S N Smirnov, Misha Balabas
    Abstract:

    The use of anti-relaxation coatings in alkali Vapor cells yields substantial performance improvements compared to a bare glass surface by reducing the probability of spin relaxation in wall collisions by several orders of magnitude. Some of the most effective anti-relaxation coating materials are alpha-olefins, which (as in the case of more traditional paraffin coatings) must undergo a curing period after cell manufacturing in order to achieve the desired behavior. Until now, however, it has been unclear what physicochemical processes occur during cell curing, and how they may affect relevant cell properties. We present the results of nondestructive Raman-spectroscopy and magnetic-resonance investigations of the influence of alkali Metal Vapor (Cs or K) on an alpha-olefin, 1-nonadecene coating the inner surface of a glass cell. It was found that during the curing process, the alkali Metal catalyzes migration of the carbon-carbon double bond, yielding a mixture of cis- and trans-2-nonadecene.

  • polarized alkali Metal Vapor with minute long transverse spin relaxation time
    2010
    Co-Authors: Misha Balabas, Todor Karaulanov, M P Ledbetter, Dmitry Budker
    Abstract:

    We demonstrate lifetimes of Zeeman populations and coherences in excess of 60 sec in alkali-Metal Vapor cells with inner walls coated with an alkene material. This represents 2 orders of magnitude improvement over the best paraffin coatings. We explore the temperature dependence of cells coated with this material and investigate spin-exchange relaxation-free magnetometry in a room-temperature environment, a regime previously inaccessible with conventional coating materials.

  • magnetometry with millimeter scale antirelaxation coated alkali Metal Vapor cells
    2006
    Co-Authors: Misha Balabas, Dmitry Budker, John Kitching, Peter D D Schwindt, J E Stalnaker
    Abstract:

    Dynamic nonlinear magneto-optical-rotation signals with frequency- and amplitude-modulated laser light have been observed and investigated with a spherical glass cell of 3 mm diameter containing Cs Metal with inner walls coated with paraffin. Intrinsic Zeeman relaxation rates of γ/(2π)≈20 Hz and lower have been observed. Favorable prospects of using millimeter-scale coated cells in portable magnetometers and secondary frequency references are discussed.

Manyalibo J. Matthews - One of the best experts on this subject based on the ideXlab platform.

  • Metal Vapor micro-jet controls material redistribution in laser powder bed fusion additive manufacturing
    2017
    Co-Authors: Sonny Ly, Saad A Khairallah, Gabriel M. Guss, Alexander M. Rubenchik, Manyalibo J. Matthews
    Abstract:

    The results of detailed experiments and finite element modeling of Metal micro-droplet motion associated with Metal additive manufacturing (AM) processes are presented. Ultra high speed imaging of melt pool dynamics reveals that the dominant mechanism leading to micro-droplet ejection in a laser powder bed fusion AM is not from laser induced recoil pressure as is widely believed and found in laser welding processes, but rather from Vapor driven entrainment of micro-particles by an ambient gas flow. The physics of droplet ejection under strong eVaporative flow is described using simulations of the laser powder bed interactions to elucidate the experimental results. Hydrodynamic drag analysis is used to augment the single phase flow model and explain the entrainment phenomenon for 316 L stainless steel and Ti-6Al-4V powder layers. The relevance of Vapor driven entrainment of Metal micro-particles to similar fluid dynamic studies in other fields of science will be discussed.

  • Denudation of Metal powder layers in laser powder bed fusion processes
    2016
    Co-Authors: Manyalibo J. Matthews, Saad A Khairallah, Gabriel M. Guss, Phillip J. Depond, Alexander M. Rubenchik, Wayne E. King
    Abstract:

    Understanding laser interaction with Metal powder beds is critical in predicting optimum processing regimes in laser powder bed fusion additive manufacturing of Metals. In this work, we study the denudation of Metal powders that is observed near the laser scan path as a function of laser parameters and ambient gas pressure. We show that the observed depletion of Metal powder particles in the zone immediately surrounding the solidified track is due to a competition between outward Metal Vapor flux directed away from the laser spot and entrainment of powder particles in a shear flow of gas driven by a Metal Vapor jet at the melt track. Between atmospheric pressure and ∼10 Torr of Ar gas, the denuded zone width increases with decreasing ambient gas pressure and is dominated by entrainment from inward gas flow. The denuded zone then decreases from 10 to 2.2 Torr reaching a minimum before increasing again from 2.2 to 0.5 Torr where Metal Vapor flux and expansion from the melt pool dominates. The dynamics of the denudation process were captured using high-speed imaging, revealing that the particle movement is a complex interplay among melt pool geometry, Metal Vapor flow, and ambient gas pressure. The experimental results are rationalized through finite element simulations of the melt track formation and resulting Vapor flow patterns. The results presented here represent new insights to denudation and melt track formation that can be important for the prediction and minimization of void defects and surface roughness in additively manufactured Metal components.

P W Fuerschbach - One of the best experts on this subject based on the ideXlab platform.

  • probing temperature during laser spot welding from Vapor composition and modeling
    2003
    Co-Authors: X He, T Debroy, P W Fuerschbach
    Abstract:

    Measurement of weld pool temperature during laser spot welding is a difficult task because of the short pulse duration, often lasting only a few milliseconds, highly transient nature of the process, and the presence of a Metal Vapor plume near the weld pool. This article describes recent research to estimate weld pool temperatures experimentally and theoretically. Composition of the Metal Vapor from the weld pool was determined by condensing a portion of the Vapor on the inner surface of an open ended quartz tube which was mounted perpendicular to the sample surface and coaxial with the laser beam. It was found that iron, chromium, and manganese were the main Metallic species in the Vapor phase. The concentrations of Fe and Cr in the Vapor increased slightly while the concentration of Mn in the Vapor decreased somewhat with the increase in power density. The Vapor composition was used to determine an effective temperature of the weld pool. A transient, three-dimensional numerical heat transfer and fluid f...

  • probing temperature during laser spot welding from Vapor composition and modeling
    2003
    Co-Authors: T Debroy, P W Fuerschbach
    Abstract:

    Measurement of weld pool temperature during laser spot welding is a difficult task because of the short pulse duration, often lasting only a few milliseconds, highly transient nature of the process, and the presence of a Metal Vapor plume near the weld pool. This article describes recent research to estimate weld pool temperatures experimentally and theoretically. Composition of the Metal Vapor from the weld pool was determined by condensing a portion of the Vapor on the inner surface of an open ended quartz tube which was mounted perpendicular to the sample surface and coaxial with the laser beam. It was found that iron, chromium, and manganese were the main Metallic species in the Vapor phase. The concentrations of Fe and Cr in the Vapor increased slightly while the concentration of Mn in the Vapor decreased somewhat with the increase in power density. The Vapor composition was used to determine an effective temperature of the weld pool. A transient, three-dimensional numerical heat transfer and fluid flow model based on the solution of the equations of conservation of mass, momentum and energy was used to calculate the temperature and velocity fields in the weld pool as a function of time. The experimentally determined geometry of the spot welds agreed well with that determined from the computed temperature field. The effective temperature determined from the Vapor composition was found to be close to the numerically computed peak temperature at the weld pool surface. Because of the short process duration and other serious problems in the direct measurement of temperature during laser spot welding, estimating approximate values of peak temperature from Metal Vapor composition is particularly valuable.

M V Romalis - One of the best experts on this subject based on the ideXlab platform.

  • tunable atomic magnetometer for detection of radio frequency magnetic fields
    2005
    Co-Authors: Igor M. Savukov, M V Romalis, Scott J Seltzer, Karen L Sauer
    Abstract:

    We describe an alkali-Metal magnetometer for detection of weak magnetic fields in the radio-frequency (rf) range. High sensitivity is achieved by tuning the Zeeman resonance of alkali atoms to the rf frequency and partially suppressing spin-exchange collisions in the alkali-Metal Vapor. We demonstrate magnetic field sensitivity of 2f T=Hz 1=2 at a frequency of 99 kHz with a resonance width of 400 Hz. We also derive a simple analytic expression for the fundamental limit on the sensitivity of the rf magnetometer and show that a sensitivity of about 0:01 fT=Hz 1=2 can be achieved in a practical system with a measurement volume of 200 cm 3 .

  • effects of spin exchange collisions in a high density alkali Metal Vapor in low magnetic fields
    2005
    Co-Authors: Igor M. Savukov, M V Romalis
    Abstract:

    Spin-exchange collisions often play a dominant role in the broadening of Zeeman resonances in an alkali-Metal Vapor. Contrary to intuitive expectations, at high alkali-Metal densities this broadening can be completely eliminated by operating in a low magnetic field, allowing construction of ultrasensitive atomic magnetometers. We describe a detailed study of the Zeeman resonance frequencies and linewidths as a function of the magnetic field, alkali-Metal density, and the degree of spin polarization of the atoms. Due to the nonlinear nature of the density matrix equations describing the spin-exchange collisions both the gyromagnetic ratio and the linewidth change as a function of the polarization. The results of experimental measurements are in excellent agreement with analytical and numerical solutions of the density matrix equations.

  • Nuclear spin gyroscope based on an atomic comagnetometer
    2005
    Co-Authors: THOMAS W KORNACK, R K Ghosh, M V Romalis
    Abstract:

    We describe a nuclear spin gyroscope based on an alkali-Metal-noble-gas comagnetometer. Optically pumped alkali-Metal Vapor is used to polarize the noble-gas atoms and detect their gyroscopic precession. Spin precession due to magnetic fields as well as their gradients and transients can be cancelled in this arrangement. The sensitivity is enhanced by using a high-density alkali-Metal Vapor in a spin-exchange relaxation free regime. With a K-3He comagnetometer we demonstrate rotation sensitivity of 5 x 10(-7) rad s(-1) Hz(-1/2), equivalent to a magnetic field sensitivity of 2.5 fT/Hz(1/2). The rotation signal can be increased by a factor of 10 using 21Ne with a smaller magnetic moment. The comagnetometer is also a promising tool in searches for anomalous spin couplings beyond the standard model.