Session C8: Invited Session: Advances in Atomic Spectroscopy

Spectroscopy of Highly Charged Ions for Astrophysics, Plasma Science, and Fundamental Science

The need for accurate atomic data of highly charged ions is spread across many branches of physics. The discovery of x-ray emission from various astrophysical objects produced by charge exchange of neutral species with highly charged ions has brought awareness that the atomic data underlying line formation is seriously inadequate, and laboratory spectroscopy is needed to advance the field. Similarly, the excitation cross sections for various L-shell emission lines of iron do not yet match the quality of the astrophysical data, thus limiting the diagnostic information that can be derived from orbiting observatories. Diagnosing the high-temperature plasmas expected to be produced by the ITER tokamak will require the development of diagnostics based on the spectroscopic emission of highly charged tungsten ions. Detailed spectroscopic studies of highly charged tungsten are now underway. Highly charged ions also provide a means for testing fundamental physics. Spectroscopic studies of U$^{89+}$ provided tests of the two-loop QED terms on par with those provided by laser spectroscopy of atomic hydrogen, while measurements of the 1s hyperfine splitting of various isotopes up to Bi$^{80+}$ have yielded data that until now have not been fully explained. This talk will point out current areas of research on highly charged ions performed on electron beam ion traps, synchrotron and free-electron x-ray lasers, and the Chandra X-ray Observatory, placing emphasis on unresolved issues and novel results.   

Francium Spectroscopy for Weak Interaction Studies

Francium, a radioactive element, is the heaviest alkali. Its atomic and nuclear structure makes it an ideal laboratory to study the weak interaction. Laser trapping and cooling in-line with the superconducting LINAC accelerator at Stony Brook opened the precision study of its atomic structure. I will present our proposal and progress towards weak interaction measurements at TRIUMF, the National Canadian Accelerator in Vancouver. These include the commissioning run of the Francium Trapping Facility, hyperfine anomaly measurements on a chain of Fr isotopes, the nuclear anapole moment through parity non-conserving transitions in the ground state hyperfine manifold. These measurements should shed light on the nucleon-nucleon weak interaction. This work is done by the FrPNC collaboration: S. Aubin College of William and Mary, J. A. Behr TRIUMF, R. Collister U. Manitoba, E. Gomez UASLP, G. Gwinner U. Manitoba, M. R. Pearson TRIUMF, L. A. Orozco UMD, M. Tandecki TRIUMF, J. Zhang UMD   

Positive Ion Properties from Spectroscopy of High-L Rydberg levels with the RESIS Method

All atoms and ions have many singly-excited levels with large values of angular momentum (L \textgreater 5). The existence of these nearly hydrogenic levels plays an important role in dynamic processes, but the details of their binding energies are often ignored since they correspond to very small quantum defects ($\delta $ \textless 0.001) and are very difficult to observe with standard spectroscopic methods. One very general method that has been developed specifically to explore the spectroscopy of these high-L levels is the RESIS, or Resonant Excitation Stark Ionization Spectroscopy method. With this technique, high-L Rydberg levels formed by charge capture in a fast atom or ion beam are resonantly excited upwards by a laser, and the upper level so populated is then Stark Ionized and the resulting ion collected with high efficiency. Because the laser transition is upwards, selection rules do not limit the angular momentum of detected levels, and many different high-L levels can be detected, resolved by the small differences between their excitation energies and the hydrogenic transition energy. Once selectively detected in this way, RF/Optical double resonance methods can measure the binding energy differences between adjacent levels with high precision. The binding energies of these high-L levels are a sensitive indicator of many properties of the positive ion binding them, such as polarizabilites and permanent electric moments. Since these properties are otherwise difficult to measure and can be difficult to calculate with confidence, the information derived from RESIS spectroscopy can provide tests of advanced theoretical methods and input to applications involving long-range interactions of atoms or ions. Two recent studies illustrate the method. One determined the dipole and quadrupole polarizabilities of the Rn-like Th$^{4+}$ ion by measuring the binding energy differences between n$=$37 Rydberg levels of Th$^{3+}$ with L$=$8-15 [1]. Another determined the quadrupole and hexadecapole moments and dipole and quadrupole polarizabilities of the Fr-like Th$^{3+}$ ion by mapping out the complex pattern of binding energies of n$=$28 Rydberg levels of Th$^{2+}$ with L$=$9-12 [2]. \\[4pt] [1] Julie A. Keele, Chris. S. Smith, and S.R. Lundeen, Phys. Rev. A \textbf{85}, 064502 (2012)\\[0pt] [2] Julie A. Keele, Chris S. Smith, and S.R. Lundeen, Phys. Rev. A \textbf{88}, 022502 (2013)   

Tests of Fundamental Symmetries with Atomic Dysprosium

While dysprosium (Dy) is arguably among the most complex atoms in terms of spectroscopy, it has proven to be a useful system for testing fundamental physics. In Dy, there is a pair of long-lived excited non-Rydberg opposite-parity states of the same total electronic angular momentum (J=10) that are separated in energy, depending on the isotope and hyperfine component, by anywhere between 3 MHz and a few GHz (with energies expressed in frequency units) in the absence of external fields. The levels may be further manipulated with external fields, for instance, applying 1.4 G brings certain sublevels to a crossing, so that one can work with a particularly ``clean'' realization of quantum-mechanical two-level system. Moreover, the near degeneracy allows measuring the difference in the energies of the levels directly enabling sensitive measurements and exotic-physics searches with relaxed requirements on atomic clocks in terms of the fractional frequency stability. Over the years, Dy has been used to set stringent limits on physics beyond the standard model [1]: a possible temporal variation of the fine-structure constand $\alpha$, changes in $\alpha$ induced by the changes of the gravitational potential of the Sun (exploiting the eccentricity of the Earth's orbit), certain types of violations of the Lorentz invariance and the Einstein's Equivalence Principle, etc. Ongoing experiments with Dy aim at measuring atomic parity violation in a chain of isotopes and hyperfine components; Dy may also prove to be a system of interest in searches for various exotic particles and fields permeating our galaxy, for instance, light scalar fields such as axions [1,2].\\[4pt] [1] See detailed bibliography at http://budker.berkeley.edu/\\[0pt] [2] Y. V. Stadnik and V. V. Flambaum arXiv:1312.6667