2s2p 1P Research Articles

Calculation of the Differential Breit–Rosenthal Effect in the 6s6p 3P1,2 States of Hg

Studies of the hyperfine anomaly has found a renewed interest with the recent development of techniques to study the properties of long chains of unstable nuclei. By using the hyperfine structure for determining the nuclear magnetic dipole moments, the hyperfine anomaly puts a limit to the accuracy. In this paper, the differential Breit–Rosenthal effect is calculated for the 6s6p3P1,2 states in 199Hg as a function of the change in nuclear radii, using the MCDHF code, GRASP2018. The differential Breit–Rosenthal effect was found to be of the order of 0.1%fm−2, in most cases much less than the Bohr-Weisskopf effect. The results also indicate that large calculations might not be necessary, with the present accuracy of the experimental values for the hyperfine anomaly.

Absolute frequency measurement of an Yb optical clock at the 10−16 level using International Atomic Time

We report on the absolute frequency measurement of the 6s2 1S0–6s6p 3P0 transition in 171Yb with a fractional uncertainty of 7.3 × 10–16. A global positioning system carrier phase frequency transfer was established between National Institute of Metrology of China and East China Normal University, which linked the optical frequency of the ECNU Yb1 clock to the second in the International System of Units (SI) through international atomic time. Frequency measurements were carried out in 15 separate days with a total time over 3.8 × 105 s. The absolute frequency was determined to be 518 295 836 590 863.30(38) Hz. Our result is in good agreement with the recommended value in neutral Yb as a secondary representation of the SI second endorsed by the International Committee for Weights and Measures.

Effects of the FEL Fluctuations on the 2s2p Li+ Auto-Ionization Lineshape

The photoionization of Lithium (Li+) via its doubly-excited state 2s2p 1P in intense free electron laser (FEL) radiation is studied. A recently developed perturbative statistical description of the atomic dynamics is used to calculate the ionization yield. It is observed that the FEL temporal fluctuations affect the lineshape significantly, strongly dependent on the product of the pulse’s coherence time with its intensity, ∼τcI0, which is a measure of the effect of the field in one correlation time. The weak-field long-pulse asymmetric resonant Fano-profile is broadened to resemble a Voight profile. As the intensity increases, the subsequent ionization of Li2+ takes over and causes further distortion of the lineshape for Li+.

Linear polarization of anisotropically excited x-ray lines from the n = 2 complex in He-like Ar16+

High-resolution x-ray spectra were recorded at the National Institute of Standards and Technology electron beam ion trap (EBIT) using two Johann-type crystal spectrometers, with their dispersion planes oriented parallel and perpendicular to the beam direction. The linear polarizations of the 1s2 − 1s2l transitions in He-like argon ions were determined from the measured spectra at electron beam energies of 3.87 and 7.91 keV. The theoretical analysis was performed using detailed collisional-radiative modeling of the non-Maxwellian EBIT plasma with the NOMAD code modified to account for magnetic sublevel atomic kinetics. Effects influencing the polarizations of the observed 1s2 − 1s2l lines were investigated, including radiative cascades, the 1s2 1S0 − 1s2s 1S0 two-photon transition, and the charge exchange recombination of H-like argon ions. With these included, the measured polarizations of the resonance (1s2 1S0 − 1s2p 1P1), intercombination (1s2 1S0 − 1s2p 3P1), and forbidden lines (1s2 1S0 − 1s2s 3S1, 1s2 1S0 − 1s2p 3P2 ) were found to be in good agreement with the calculations.

Characterisation and feasibility study for superradiant lasing in 40Ca atoms.

Superradiant active clocks operating on narrow linewidth clock transitions are predicted to achieve precision orders of magnitude higher than any currently existing optical atomic clocks. We introduce a theory of superradiant lasing and implement it for the example of 40Ca atoms. The presented model, however, is valid for any two- or three-level system in an optical lattice. We perform a feasibility analysis and suggest a set of parameters for the experimental fulfillment of superradiant lasing in Ca. Moreover, we present an overview of different magic wavelengths for the 4s2 1S0 ↔ 4s4p3P1 (mJ = 0) transition in Ca for different polarizations and a robustness analysis of these magic conditions. We also report the magic-zero wavelengths for the 4s4p3P1, mJ = 0 state.

Most Intense X-Ray Lines of the Helium Isoelectronic Sequence for Plasmas Diagnostic

We report accurate wavelengths for the three most intense lines (resonance line: 1s2 1S0 - 1s2p 1P1, intercombination line: 1s2 1S0 - 1s2p 3P1 and forbidden line: 1s2 1S0 - 1s2s 3S1) along with wavelengths for the 1s2 1S0 - 1snp1P1 and 1S0 - 1snp3P2 (2 ≤ n ≤ 25) transitions in He-like systems (Z = 2 – 13). The first spectral lines that belong to the above transitions are established in the framework of the Screening Constant per Unit Nuclear Charge method. The results obtained agree excellently with various experimental and theoretical literature data. The uncertainties in wavelengths between the present calculations and the available literature data are less than 0.004Å. A host of new data listed in this paper may be of interest in astrophysical and laboratory plasmas diagnostic.

RABBITT attoclock for the direct measurement of ionization phases

SynopsisWe use a circularly polarized attosecond pulse train (APT) together with a weak replica of the fundamental circularly polarized infra-red (IR) field to reconstruct the ionization phase of the dipole allowed (2s2p)1P° resonance in atomic helium by analyzing the momentum distribution of the ionized photoelectrons within the polarization plane.

Local time dependence of the magnetic sublevel population and polarization of fluorescence radiation

We investigate the time-dependence magnetic sublevel population and polarization of x-ray photoemission for the 1s2p 3P2,1 → 1s2 1S0 lines of an exemplary ion Fe24+ due to impact excitation by a longitudinally polarized electron beam. The analysis is performed based on the fully relativistic distorted-wave approximation and the magnetic sublevel-to-magnetic sublevel collisional-radiative model. The radiative cascade process and Breit interaction are considered to make the results more precise. The time evolution of the magnetic sublevel populations and circular polarization properties are discussed. Our results reveal for the first time that the variations of the magnetic sublevel populations demonstrate a pattern when the time is shorter than 103 ps; some of the populations increase rapidly, while the others remain relatively constant. These dramatic influences also bring about notable changes in the polarization properties of fluorescence emission. We compare our results with other theoretical predictions and find good consistency. This work provides new insight into the fundamentals of x-ray radiation and further prompts the application of fluorescence polarization in plasma diagnostics.

Kinetics of a Collision-Induced Photon Echo

The nonmonotonic kinetics of a collision-induced photon echo has been investigated for a number of buffer atoms. The collision-induced photon echo was generated at the 174Yb (6s2) 1S0 ↔ (6s6p) 3P1 (0 ↔ 1) transition by a pair of linearly and mutually orthogonally polarized resonant radiation pulses in ytterbium vapor and its mixtures with He, Ne, Ar, Kr, and Xe. The kinetics of the conventional photon echo generated by pulses with identical linear polarizations was recorded in the same mixtures. The derived decay rate constants for both types of echo are equal to within the measurement errors. For the collisions of 174Yb atoms between themselves and with other ytterbium isotopes in a natural mixture of isotopes, an upper limit for the anisotropy parameter has been estimated, 0.22 ± 0.07 of the photon echo signal decay rate.

Photon echo in the ytterbium vapour induced at transition by the relaxation anisotropy of collisions with noble gases

A collision-induced photon echo (PE) was formed at the 174Yb (6s2) 1S0—(6s6p) 3P1 transition by two resonant radiation pulses polarized linearly and mutually orthogonally. The noble gases He, Ne, Ar, Kr and Xe were used as collision partners for excited 174Yb atoms. The nonmonotonous decay kinetics of collision-induced PE was detected. The ordinary PE formed by identical linear polarization pulses at the same experimental conditions showed a monotonous decay for the time delays between 80 and 300 ns. The anisotropy parameters for the collisions of 174Yb atoms with Ne, Ar, Kr and Xe atoms increase with the buffer atom mass and are between 15% and 20% of the corresponding homogeneous line broadening values.

Dominance of the density effects in the magnetic sublevel population and circular polarization of x-ray radiation

On the basis of the fully relativistic distorted-wave treatment of impact excitation by a longitudinally polarized electron beam, we have assessed the influence of density effects on the magnetic sublevel population and circular polarization of x-ray radiation, taking the 1s2p 3P2 1s2 1S0 line of selected He-like Ne8+, Ar16+, and Kr34+ ions as an example. Starting from the most general method of rate equation, we carried out specific analytic expressions in terms of the magnetic sublevel-to-magnetic sublevel collisional-radiative model, corresponding to different states. It is shown that the density contributions to the magnetic sublevel population can be considerable. These dramatic influences also lead to a remarkable decrease in the circular polarization of x-ray radiation, yet the character of which weakens as the incident energy and/or atomic number increases. The Breit interaction and radiative cascade contributions are also estimated, and found to be generally important in these systems. These findings originate a better understanding of the fundamentals of x-ray radiation arising from various kinds of plasmas. Comparisons of our results with other theoretical predictions, when available, are made.

Reevaluation of the nuclear electric quadrupole moment for Sr87 by hyperfine structures and relativistic atomic theory

The values of nuclear electric quadrupole moment are different by about 7% for 87Sr nucleus between the recommended value [N. J. Stone, At. Data Nucl. Data Tables 111-112, 1 (2016); P. Pyykko, Mol. Phys. 116, 1328 (2018)] and earlier results [e.g. A. M. Matensson-Pendrill, J. Phys. B: At. Mol. Opt. Phys. 35, 917 (2002); K. Z. Yu et al., Phys. Rev. A 70, 012506 (2004)]. In this work, we reported a new value, Q(87Sr) = 328(4) mb, making use of our calculated electric field gradients produced by electrons at nucleus in combination with experimental values for hyperfine structures of the 5s5p 3P1,2 states of the neutral Sr atom. In the framework of the multi-configuration Dirac-Hartree-Fock theory, the electron correlations were taken into account systematically so as to control the uncertainties of the electric field gradient at about 1% level. The present result is different from the recommended value, but in excellent agreement with those by Matensson-Pendrill and Yu et al.. We would recommend the present Q value as a reference for 87Sr.

Triplet emission of atomic ytterbium isolated in a xenon matrix

The electronic transitions of ytterbium atoms in a solid Xe matrix grown at 4.8 K are investigated. Absorption bands are detected in the regions of the gas-phase 6s2 1S0 → 4f135d6s2 and 6s2 1S0 → 6s6p 1P1 transitions. Both bands indicate that Yb atoms occupy multiple trapping sites, of which three are identified. Emission induced by the 6s2 1S0 → 6s6p 1P1 excitation is found to be concentrated entirely in the region of the 6s6p 3PJ → 6s2 1S0 decay, whereas the singlet emission is completely quenched. Multiple emission peaks are observed and the effects of annealing and prolonged irradiation on their amplitudes are found to be significant and are interpreted as a consequence of Yb population transfer from one type of site to another. Modeling of the ground-state site structure and stability predicts three Yb/Xe occupation types, substitutional (ss), tetravacancy (tv) and hexavacancy (hv), in order of decreasing stability. Their tentative associations with observed absorption and emission features are discussed. Time correlated single photon spectroscopy is used to determine the lifetimes of the individual emission bands. They are found to be different from each other with indications of a mixture of short- and long- lived 6s6p 3PJ fine-structure components and demonstrate distinct temperature dependencies. A dramatic decrease in the lifetime of the emission peak tentatively assigned to the most stable site with temperature is explained by a competition between the radiative and non-radiative decay paths of the 6s6p 3P1 state. The mechanism of the latter can be attributed to electron–phonon coupling as confirmed by a model of the temperature-dependence of the lifetime.The electronic transitions of ytterbium atoms in a solid Xe matrix grown at 4.8 K are investigated. Absorption bands are detected in the regions of the gas-phase 6s2 1S0 → 4f135d6s2 and 6s2 1S0 → 6s6p 1P1 transitions. Both bands indicate that Yb atoms occupy multiple trapping sites, of which three are identified. Emission induced by the 6s2 1S0 → 6s6p 1P1 excitation is found to be concentrated entirely in the region of the 6s6p 3PJ → 6s2 1S0 decay, whereas the singlet emission is completely quenched. Multiple emission peaks are observed and the effects of annealing and prolonged irradiation on their amplitudes are found to be significant and are interpreted as a consequence of Yb population transfer from one type of site to another. Modeling of the ground-state site structure and stability predicts three Yb/Xe occupation types, substitutional (ss), tetravacancy (tv) and hexavacancy (hv), in order of decreasing stability. Their tentative associations with observed absorption and emission features are discu...

State‐selective single‐electron capture in 30‐keV N3+–He collisions

The cold‐target recoil‐ion momentum spectroscopy has been employed to study the single‐electron‐capture processes in collisions of N3+ ions with He atoms at an impact energy of 30 keV. From the longitudinal momentum spectrum of recoil ions, the different electronic configuration was identified, and the metastable projectile ions were distinguished. For the ground‐state N3+(2s2 1S) projectile, the single‐electron capture into the N2+(2s22p 2P) state is the dominant reaction channel, whereas for the metastable‐state N3+(2s2p 3P) projectile, the single‐electron capture into the N2+(2s2p2 2D) state is the main reaction channel. The fraction of the metastable‐state N3+(2s2p 3P) of the incident projectile beam is about 46%. The relative differential cross sections for the capture to different orbitals of N3+ ions are obtained and are compared with other experiments at low energy and the predictions of the classical over‐the‐barrier model.

A compact and robust cooling laser system for an optical strontium lattice clock.

We present a simple and robust laser system for two-color, narrow-line cooling on the 87Sr (5s2)1S0 → (5s5p)3P1 transition. Two hyperfine lines of this transition are addressed simultaneously with light from a single laser source, using sidebands created by an electro-optical phase modulator. A tapered amplifier system provides laser powers up to 90 mW. We show that amplification does not affect the phase modulation of the laser. This compact and robust laser system offers excellent reliability. Therefore, it is especially well suited for transportable and spaceborne optical clocks. The design offers the potential to be miniaturized into a fully integrated package.

The use of geometric effects in diagnosing ion density in ICF-related dot spectroscopy experiments

We describe a method to calculate the ion density of High Energy Density (HED) cylindrical plasmas used in dot spectroscopy experiments. This method requires only spectroscopic measurements of the Heα region obtained from two views (Face-on and Side-on). We make use of the fact that the geometry of the plasma affects the observed flux of optically thick lines. The ion density can be derived from the aspect ratio (height-to-radius) of the cylinder and the optical depth of the Heα-y line (1s2p 3P1 → 1s2 1S0). The aspect ratio and the optical depth of the y line are obtained from the spectra using ratios measured from the two directions of emission of the optically thick Heα-w line (1s2p 1P1 → 1s2 1S0) and the ratio of the optically thick to thin lines. The method can be applied to mid-Z elements at ion densities of 1019–1020cm−3 and temperatures of a the order of keV, which is a relevant regime for Inertial Confinement Fusion (ICF) experiments.

Near-infrared Zeeman spectroscopy for the spatially resolved measurement of helium emission spectra in Heliotron J

A passive spectroscopic method that can measure spatially resolved emission spectra only by observing from a single diagnostic port without assuming plasma symmetry was applied to the stellarator-heliotron device Heliotron J. The emission spectra from the inboard and outboard sides were separated using the difference in their Zeeman effects. On the basis of the fact that in a spectrum as a function of the wavelength, the magnitude of the wavelength splitting by the Zeeman effect relative to the Doppler broadening increases with the wavelength, the method was applied to a near-infrared helium emission line (He I 1s2s 3S−1s2p 3P, 1083 nm), and it was confirmed that the uncertainty in the separated spectra was reduced compared with that in the application to visible emission lines. From the emissivity of the separated spectra, the local recycling flux was evaluated using the inverse photon efficiency method.

Measurement of Auger electrons emitted through Coster–Kronig transitions under irradiation of fast [formula omitted] ions

We measured the yield of Auger electrons emitted through Coster–Kronig transitions from Rydberg states 1s2p(3P)nl (n=7,8) and 1s22p(2P)nl (n=5,6,7) of emergent atomic ions Cq+ under irradiation of 3.5-MeV/atom C+ and C2+ ions on thin C foil targets. The Auger electron yields are suppressed for C2+ irradiation compared with C+ irradiation and the relative yield becomes larger as n increases. Thus, amount of scattered electrons having lower relative energy in the projectile rest frame becomes larger. The results obtained in this study support the influence of projectile velocity on the cluster effect of secondary electron yields.

Investigation of Optical Ionization of Strontium via 5s21S0 ⟶ 5s5p 3P1° ⟶ 5s5d 3D2 ⟶ 4dnp (or 4ndf, n = 39) for Isotope Selectivity Enhancement

We investigated a promising three-step resonance ionization scheme of strontium (Sr) 5s21S0 ⟶ 5s5p 3P1° ⟶ 5s5d 3D2 ⟶ 4dnp (or 4dnf, n = 39) using the first-step intercombination transition for the enhancement of isotope selectivity. The power broadening observed in the 2nd transition indicates that laser power of less than 0.2 mW is sufficient for saturating this transition. Isotope separation can be successfully expected with application of the 3rd transition due to the narrow width of the 4dnp (or 4dnf, n = 39) autoionization level, paving the way for analysis of trace 90Sr in environmental applications.

Kinetics of two-pulsed photon echo formed on the 0–1 transition: isotropic and anisotropic collisions

The photon echo formed at the intercombination (6s2) 1S0 (6s6p) 3P1 (type 0–1) transition of ytterbium atoms 174Yb by two pulses of resonance radiation was investigated as a function of the time delay between exciting pulses (the photon echo kinetics). For exciting radiation pulses of the same linear polarization in the delay region 70–250 ns, the photon echo kinetics is close to the exponential one both in pure ytterbium and in its mixtures with buffer gases Ar and Xe. The relaxation cross sections were determined for all three cases, taking into account the isotopic composition of xenon and ytterbium. For the first time, the complex nonmonotonous kinetics of the collision-induced photon echo was observed in the same mixtures for the forming pulses of linear mutually orthogonal polarization. The relative efficiency of buffer atoms Yb (other isotopes than 174Yb), Xe and Ar in the collision-induced photon echo formation was obtained.