Session G4: Spectroscopy, Lifetimes, and Oscillator Strengths

Hyperfine quenching of the $2s^22p^{5}3s\ ^3P_2$ state of Ne-like ions

The many-body perturbation theory (RMBPT) is used to calculate energies and multipole matrix elements to evaluate hyperfine quenching of the $2s^22p^53s\ 3P_2$ state in Ne-like ions. In particular, the $^3P_2$ excited state decays to the $^1S_0$ ground state by M2 emission, while both $^1P_1$ and $^3P_1$ states decay to the ground-state by E1 emission, which is substantially faster. For odd-A nuclei, the hyperfine interaction induces admixtures of $^3P_1$ and $^1P_1$ states into the $^3P_2$ state, resulting in an increase of the $^3P_2$ transition rate and a corresponding reduction of the $^3P_2$ lifetime. We consider 22 Ne like ions with $Z$ = 14 - 94 and nuclear moment $I$ =1/2. We found that the largess hyperfine quenching contribution by a factor of 2 are for Ne-like $^{31}$P and $^{203}$Tl. The smallest (less than 1\%) induced contribution are the following Ne-like ions: $^{57}$Fe, $^{107}$Ag, $^{109}$Ag, $^{183}$W, and $^{187}$Os ions. For another 15 Ne-like ions the hyperfine quenching contribution is between 15\% and 35\%. Applications to x-ray line polarization of Ne-like lines is considered.   

Kr X-ray spectroscopy to diagnose Inertial Confinement Fusion implosions on the National Ignition Facility

X ray spectroscopy is used on the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL) to diagnose the plasma conditions in the ignition target in indirect drive Inertial Confinement Fusion (ICF) implosions [1]. A platform is being developed at NIF where small traces of krypton are used as a dopant to the fuel gas for spectroscopic diagnostics using krypton line emissions. Simulations of the krypton spectra using a small atomic fraction of krypton in direct-drive exploding pusher with a range of electron temperatures and densities show discrepancies when different atomic models are used. We use our non-local thermodynamic equilibrium (non-LTE) atomic model with a detailed fine-structure level atomic structure and collisional-radiative rates to investigate the krypton spectra at the same conditions and generate synthetic spectra with a detailed frequency-by-frequency radiation transport scheme from the emission regions of interest to analyze the experimental data and compare and contrast with the existing simulations at LLNL. [1] T. Ma, et al., RSI 87 (2016). Work supported by DOE/NNSA; Part of this work was also done under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No DE-AC52-07NA27344.   

Dielectronic Satellite Lines of L-shell Mo at LLNL EBIT

Dielectronic recombination, an important atomic process for astrophysical and laboratory plasmas, has been studied in detail for low-Z and recently for W ions. However, there are still many details missing for other materials including molybdenum (Mo). New calculations were done for Ne-like Mo dielectronic recombination transitions using the COWAN code, HULLAC, and the relativistic many-body perturbation theory method. The EBIT-I electron beam ion trap at Lawrence Livermore National Laboratory (LLNL) was used to benchmark the new calculations. EBIT-I was operated to create Ne-like Mo using a \textasciitilde 3 keV energy beam and then using lower energy beams (0.6 -- 1.2 keV) to account for dielectronic recombination. The new theoretical calculations were compared to Na-like Mo satellite spectra collected from LLNL EBIT-I experiments with consideration to polarization sensitivities.   

Single and multi photon molecular transitions of cold Rb Rydberg atoms

Microwave transitions between pair states composed of two Rb Rydberg atoms in a magneto-optical trap are investigated. This is an extension of the experiment to investigate the transition from ndnd to (n+1)d(n-2)f states, which is allowed because the (n+2)p(n-2)f state that is energetically close to ndnd state is admixed into the ndnd state as a result of the dipole-dipole induced configuration interaction between the two states. The microwave transition is from the (n+2)p(n-2)f part of the wavefunction to the (n+1)d(n-2)f state. The microwave drives a transition from (n+2)p to another state in one atom with the other atom remaining a spectator in the (n-2)f state. In this follow up experiment, a series of one, two, and three photon microwave transitions that occur due to the same mechanism was observed. More specifically, microwave transitions from ndnd to (n+3)s(n-2)f, (n+3)p(n-2)f, and (n+4)s(n-2)f as well as from nsns to (n-1)d(n-2)p were observed. The measured frequencies were found to agree well with the calculated values. The ac Stark shifts and transition probabilities for the transitions can be explained using a Floquet approach.   

Laser spectroscopy of fine-structure splittings in the 2$^{\mathrm{3}}$P$_{\mathrm{J}}$ levels of $^{\mathrm{4}}$He

The fine-structure splittings of the 2$^{\mathrm{3}}$P$_{\mathrm{J}}$ (J$=$0, 1, 2) levels of $^{\mathrm{4}}$He is of great interest for tests of quantum electrodynamics and for the determination of the fine structure constant $\alpha $. Here we report our recent studies on the fine-structure splitting intervals. The metastable helium atoms are prepared by RF discharge and are collimated by transverse cooling. The laser spectroscopy is performed via 2$^{\mathrm{3}}$P$_{\mathrm{J\thinspace }}$- 2$^{\mathrm{3}}$S$_{\mathrm{1}}$ transitions at 1083nm. The 2$^{\mathrm{3}}$P$_{\mathrm{0\thinspace }}$- 2$^{\mathrm{3}}$P$_{\mathrm{2}}$ and2$^{\mathrm{3}}$P$_{\mathrm{1\thinspace }}$- 2$^{\mathrm{3}}$P$_{\mathrm{2}}$ intervals are determined to be 31 908 130.98(13) kHz and 2 291 177.56(19) kHz, respectively. Both intervals show good agreements with the theoretical calculations. Progress towards measurements on the absolute frequency of 2$^{\mathrm{3}}$P$_{\mathrm{J\thinspace }}$- 2$^{\mathrm{3}}$S$_{\mathrm{1}}$ on $^{\mathrm{4}}$He will be reported.   

Measurement of hyperfine structure and isotope shifts in the $8p$ excited states of thallium and the $7p$ excited states of indium using two-step laser spectroscopy

Using a two-color, two-step vapor cell spectroscopy technique we have completed measurements of hyperfine splittings of 8$p$ states in $^{205}$Tl and $^{203}$Tl, as well as the $7s-8p$ transition isotope shifts. The same experimental scheme has been used to measure the hyperfine splitting of the $^{115}$In 7$p_{1/2}$ state and the hyperfine $a, b, c$ constants within the 7$p_{3/2}$ state. An external-cavity diode laser locked to the 1st step transition excites atoms to an intermediate state and a second, red laser diode overlaps the first within a heated atomic vapor cell in both a co-propagating and counter-propagating configuration. Analysis of subsequent Doppler-free absorption spectra of the second-step transitions (7$s_{1/2}$ $\rightarrow$ 8$p_{1/2,3/2}$ in thallium and 6$s_{1/2}$ $\rightarrow$ 7$p_{1/2,3/2}$ in indium) allows us to extract both hyperfine and isotope shift information with uncertainties well below 1 MHz. Frequency modulation of the red laser provides convenient \textit{in situ} frequency calibration. For the case of thallium $^{205}$Tl 8$p_{3/2}$ state hyperfine splitting, our results disagree with older measurements and show a well-resolved hyperfine anomaly not previously observed for this state.   

Direct search for the thorium-229 nuclear isomeric transition with a pulsed VUV laser

The nucleus of thorium-229 has an exceptionally low-energy isomeric transition in the vacuum-ultraviolet (VUV) spectrum around $7.8 \pm 0.5$eV [1]. While inaccessible to standard nuclear physics techniques, there are various prospects for a laser-accessible nuclear transition. Our direct search for the transition uses thorium-doped crystals as samples. In a previous experiment [2] at the Advanced Light Source (ALS) synchrotron, LBNL, we were able to exclude a large portion of the transition lifetime-vs.-frequency region-of-interest (ROF) [3]. Here, we will report on our ongoing efforts of a search using a pulsed VUV laser system as light source, which allows us to enhance our sensitivity up to $10^4 \times$ over the ALS and extend the accessible frequency range over the entire ROF [3]. An updated exclusion region will be presented. \\[2ex] {[1]} B. R. Beck et al.: LLNL-PROC-415170 (2009)\\ {[2]} J. Jeet et al.: Phys. Rev. Lett. 114, 253001 (2015)\\ {[3]} E. V. Tkalya et al.: Phys. Rev. C 92, 054324 (2015)   

High precision spectroscopy of p-state Rubidium Rydberg molecules

In an ultracold gas the scattering interaction of a ground state atom and the highly excited electron of a Rydberg atom gives rise to an oscillatory potential that supports molecular bound states. We use high resolution time-of-flight spectroscopy over a range of several 10GHz to precisely determine the binding energies and lifetimes of molecular states in the vicinity of the 25P-state. For the so called butterfly molecules, that originate from a shape resonance in the p-wave electron-atom scattering and strongly mix high angular momentum states, we investigate their rotational structure in an external electric field allowing us to extract the precise bond length and huge dipole moments. By exciting ultralong-range Rydberg molecules we are able to observe a spin-flip of the ground state atom. This induced spin-flip is based on mixed singlet-triplet potentials containing contributions of both hyperfine states of the ground state atom. In additon, we resolve molecular states which feature strong entanglement between the orbital angular momentum of the Rydberg electron and the nuclear spin of the ground state atom due to nearly degenerate spin-orbit splitting of the Rydberg atom and hyperfine splitting in the ground state.   

The Ratio of the Resonance Line to Intercombination Line in Neonlike Ions.

We present the measurement results of the intensity ratios of astrophysically important 1s$^{\mathrm{2}}$2s$^{\mathrm{2}}$2p$^{\mathrm{5}}_{\mathrm{1/2}}$3d$_{\mathrm{3/2}}$ $\to $ 1s$^{\mathrm{2}}$2s$^{\mathrm{2}}$2p$^{\mathrm{6}}$ resonance line to the 1s$^{\mathrm{2}}$ 2s$^{\mathrm{2}}$ 2p$^{\mathrm{5}}_{\mathrm{3/2}}$ 3d$_{\mathrm{5/2}} \quad \to $ 1s$^{\mathrm{2}}$2s$^{\mathrm{2}}$2p$^{\mathrm{6}}$ intercombination line for Ne-like Kr$^{\mathrm{26+}}$ and Mo$^{\mathrm{32+}}$. The experiment was done at the EBIT-I electron beam ion trap at Lawrence Livermore National Laboratory and utilized an x-ray microcalorimeter. The Mo$^{\mathrm{32+}}$ experiment is the highest Z-measurement of such type to date, where the dominant role of the intercombination line, known to increase with Z, puts our measurement firmly into the relativistic regime. Compared to the earlier measurements of ions with lower atomic numbers, the measurement for Mo$^{\mathrm{32+\thinspace }}$shows much a closer agreement with theory. Our results support the hypothesis that the disagreement should narrow with atomic number. This implies that the disagreement with theory may be confined to the range of atomic numbers where the correlation effects are largest.