Bulletin of the American Physical Society
83rd Annual Meeting of the APS Southeastern Section
Volume 61, Number 19
Thursday–Saturday, November 10–12, 2016; Charlottesville, Virginia
Session G4: Atomic, Molecular and Optical Physics II |
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Chair: C. Sackett, University of Virginia Room: Preston Room |
Friday, November 11, 2016 10:45AM - 10:57AM |
G4.00001: An experimental determination of quantum defects of ng and nh series for Rb Jeonghun Lee, Jirakan Nunkaew, Tom Gallagher We present an experimental technique to determine ng and nh series quantum defects for Rb. The technique is based on measuring a property of the atom that depends on the field, as opposed to its square. Using the technique, we are able to measure zero field intervals between (n$+$1)d$_{\mathrm{5/2}}$ and ng/nh states for 27 $\le $ n $\le $ 30 despite the fact that the electric field can be only controlled in one direction in our setup. The ng and nh series quantum defects are extracted from the zero-field intervals. Using the quantum defects and adiabatic core polarization theory, we also obtain the scalar polarizabilities of Rb ionic core. Our results and the comparison with other results are presented. This work is supported by Air Force Office of Scientific Research. [Preview Abstract] |
Friday, November 11, 2016 10:57AM - 11:09AM |
G4.00002: Dipole-dipole Resonance Line Shapes in a Cold Rydberg Gas B. G. Richards, R. R. Jones We have explored the dipole-dipole mediated, resonant energy transfer reaction $32p_{3/2}+32p_{3/2} \rightarrow 32s+33s$ in an ensemble of cold $^{85}$Rb Rydberg atoms. Stark tuning is used to measure the population transfer probability as a function of the total electronic energy difference between the initial and final atom-pair states over a range of Rydberg densities of $2 \times 10^{8} \leq \rho \leq 4 \times 10^{9}$ cm$^{-3}$. The observed line shapes provide information on the role of beyond nearest-neighbor interactions, the range of the Rydberg atom separations, atom motion, and the electric field inhomogeneity in the sample. For short interaction times, the line-widths increase approximately linearly with Rydberg atom density and are in agreement with expectations from a two-body, nearest-neighbor interaction model. At low densities, Gaussian line shapes are observed due to electric field inhomogeneities, providing an upper limit for the field variation across the sample. At higher densities, non-Lorentzian, cusp-like line shapes characterized by sharp central peaks and broad wings reflect the random distribution of inter-atomic distances within the magneto-optical trap (MOT). [Preview Abstract] |
Friday, November 11, 2016 11:09AM - 11:21AM |
G4.00003: Observed cyclotron structure in photodetachment to excited states of the O atom John Yukich, Hannah Thigpen The $^{\mathrm{2}}$P$_{\mathrm{3/2\thinspace \thinspace }}\to $ $^{\mathrm{3}}$P$_{\mathrm{2}}$ and $^{\mathrm{2}}$P$_{\mathrm{1/2\thinspace \thinspace }}\to \quad^{\mathrm{3}}$P$_{\mathrm{2}}$ photodetachment thresholds for ions such as S$^{\mathrm{-}}$ and O$^{\mathrm{-}}$ have been examined in numerous experiments. In many of these experiments, structure in the cross section due to Zeeman and cyclotron transitions has been resolved. Our most recent experiment explores transitions to the first two excited states of the O neutral in an attempt to detect similar cyclotron and Zeeman structure. The apparatus in the experiment includes a Penning ion trap which creates, traps and stores the O$^{\mathrm{-}}$ ions, and a single-mode, tunable, amplified diode laser. For the first time in our laboratory photodetachment work, we have observed cyclotron structure in the detachment to an excited state, specifically for the $^{\mathrm{2}}$P$_{\mathrm{1/2\thinspace }}\to $ $^{\mathrm{3}}$P$_{\mathrm{0\thinspace }}$electronic transition. [Preview Abstract] |
Friday, November 11, 2016 11:21AM - 11:33AM |
G4.00004: Measurements of radially and temporally distributed laser-induced plasma parameters Ghaneshwar Gautam, Christian Parigger Laser-induced optical breakdown is generated in a mixture of ultra-high purity hydrogen and nitrogen gas inside a cell. The hydrogen and nitrogen gas mixture ratio is 9 to 1 at a pressure of 1.21 \textpm 0.03 \texttimes 10$^{\mathrm{5}}$ Pa. The radiation of a Q-switched Nd:YAG laser device, operated at its fundamental wavelength of 1064 nm, is focused to above threshold irradiance for generation of optical breakdown. For the determination of characteristic parameters of the transient micro-plasma in a gas mixture, spatially and temporally resolved line-of-sight spectra of hydrogen \textit{Balmer} series H$_{\mathrm{\alpha }}$ and H$_{\mathrm{\beta }}$ lines are recorded. The line-of-sight measurements are \textit{Abel} inverted to extract the radial distributions of electron number density and temperature. Slight asymmetries observed in the recorded data are also considered in the analysis. The plasma kernel expansion speeds of 2 \textpm 0.4 km/s and 1.5 \textpm 0.3 km/s are determined at the time delays of 100 ns and 200 ns, respectively. Shockwave expansion speeds are also determined for these time delays. Furthermore, the isentropic micro-plasma expansion model is discussed in the data analysis. [Preview Abstract] |
Friday, November 11, 2016 11:33AM - 11:45AM |
G4.00005: Phase dependent excitation of Rydberg states in static fields. Eric Magnuson, Vincent Carrat, Gallagher Tom Atomic electrons excited to energies near the ionization limit in the presence of a strong microwave (MW) field can end up in high lying Rydberg states. Analogous to attosecond and IR ionization experiments, the probability of producing these Rydberg states depends on the phase of the MW field at the time of excitation. In the presence of a MW field, we use an infrared (IR) laser to excite Lithium atoms to states near the ionization limit. Amplitude modulating the laser at the MW frequency gives us control of the phase of the MW field at which the excitation occurs. A prior experiment shows that, in an isotropic system, the phase dependent Rydberg production occurs at twice the MW frequency. Current work shows that applying a static field to break the symmetry along the IR and MW polarization produces phase dependence at the same frequency as the MW field. We experimentally explore how this effect changes with excitation energy, MW intensity and static field strength, and compare to results from a classical simulation. Future work will determine the absolute phase offset between the laser modulation and the MW field, and explore regimes with stronger fields and more deeply bound states, where the classical model breaks down. [Preview Abstract] |
Friday, November 11, 2016 11:45AM - 11:57AM |
G4.00006: Characterizing the perturbed 6snd series of Ytterbium using MW spectroscopy Fathima Niyaz, Thomas Gallagher The 6snd Rydberg series is perturbed weakly by a doubly excited state lying between the 6s26s and 6s27d states. We have used microwave transitions between 6sns-6s(n$+$1)s and 6sns-6s(n-1)d states to determine the energies of the 6snd Rydberg states of~28$\le $n$\le $40. We have analyzed the energies if the perturbed series using quantum defect theory, which allows the characterization of the perturbed series by only four parameters. The quantum defect theory model~predicts the energies to the accuracy of a few MHz. We have also made lifetime measurements of the 6snd states and recorded the forced autoionization spectra as consistency checks of our analysis. [Preview Abstract] |
Friday, November 11, 2016 11:57AM - 12:09PM |
G4.00007: High-precision measurements of the $^{87}$Rb vector polarizability Adam Fallon, Seth Berl, Charles Sackett We report progress on an experiment to measure the vector polarizability of $^{87}$Rb atoms in the $ F = 2 $ ground hyperfine state between the $D1$ and $D2$ spectral lines. The experiment uses a condensate interferometer to measure a tune-out wavelength, the light wavelength at which the ac electric polarizability of the atom equals zero. The location of the tune-out wavelength depends on the optical polarization of the light, and the vector polarizability characterizes this dependence. This can be compared to previous measurements by our group of tune-out wavelengths for the scalar polarizability alone. Measurements of the vector polarizability and tune-out wavelengths near multiple atomic states allows the identification of individual contributions to the polarizability from higher-lying states and from the core electrons. Accurate knowledge of these contributions would be useful as a theoretical benchmark and for improved analysis of atomic parity violation experiments. [Preview Abstract] |
Friday, November 11, 2016 12:09PM - 12:21PM |
G4.00008: Tomographic characterization of an atom trapping potential Edward Moan, Tanwa Arpornthip, Charles Sackett We have developed a technique to fully characterize the potential profile of an arbitrary atom trap. A cold atom cloud is loaded into a weakly-confined time-orbiting potential (TOP) trap. The atoms are optically pumped into a dark state, an energy level that does not interact with the probe laser light. A cross-sectional region of the atom cloud is reactivated by a ``sheet'' of repump light that optically pumps the atoms back into the probed energy state. The repump light sheet is roughly 100 $\mu$m thick. The reactivated region interacts with the probe laser light to create a fluorescence image. Since the light sheet is much thinner than the 2 mm-wide atom cloud, the fluorescence image obtained is a cross-section of the atom cloud. A movable light sheet allows us to generate cross-section images of the cloud at different positions. A composite image of all the cross-section images shows the complete density profile of the atom trap. This is similar to tomographic imaging used in medical imaging. From the density profile, the potential energy function can be obtained, assuming the atoms are in equilibrium. We have verified the technique with various other benchmarks, viz. direct oscillation measurements, trajectory analysis, and numerical simulation of the atom trap. [Preview Abstract] |
Friday, November 11, 2016 12:21PM - 12:33PM |
G4.00009: Characterization of nano-level coefficient of friction of oleophobic and superhydrophobic coatings on 316L SS in harsh conditions Hamza Shams, Sajid Saleem, Kanza Basit, Salman Nisar 316L SS is widely used in marine applications due to its high resistance to corrosion. This study emphasizes on investigating the commercially available superhydrophobic / oleophobic coatings applied over 316L SS and subsequently finding out the nano-level coefficient of friction. Samples of 316L SS were prepared and coated with three oleophobic coatings. After coating, one set of samples were tested in sand-storm conditions and another set in sea-breeze conditions. Lateral Force Microscopy (LFM) has been used to determine the coefficient of friction at nano-level. The coefficient of friction is associated with the amount of wear. The coefficient of friction is obtained for three states; before coating, after coating and after sand-storm / sea-breeze condition. From the comparison of results, the performance of the coating has been evaluated. The coefficient of friction changed drastically when the coated samples were exposed to sand-storm conditions whereas very little difference was observed for sea-breeze condition. Since oleophobic coating prevents a material from corrosion as well as erosion, it was seen that the coating was damaged after a considerable amount of time and it protected the base substrate from being exposed to the environment. [Preview Abstract] |
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