Bulletin of the American Physical Society
82nd Annual Meeting of the APS Southeastern Section
Volume 60, Number 18
Wednesday–Saturday, November 18–21, 2015; Mobile, Alabama
Session B1: Atomic, Molecular and Optical Physics I |
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Chair: Hauke Busch, Georgia College & State University Room: Riverview Plaza Hotel Mobile Bay Ballroom I |
Thursday, November 19, 2015 11:00AM - 11:12AM |
B1.00001: Self-Absorption Corrections for Aluminum Neutrals and Ions in Laser-Induced Plasma David Surmick, Christian Parigger Laser ablation of an aluminum surface is investigated in the study of rapidly expanding plasma and shock phenomena using time and space resolved spectroscopy. The initial 100 ns following optically-induced breakdown are of interest due to the significant number of free electrons in the plasma expansion. Breakdown is initiated using a 14 ns pulsed Nd:YAG, Q-switched laser. The experiments are performed using a gas cell containing 90 percent hydrogen and 10 percent nitrogen so that nitrogen ion and hydrogen Balmer series lines may be used to infer the electron density in addition to using neutral and ionic aluminum line width diagnostics [1]. At early time delays from plasma generation, self-absorption is likely to be present and causes spectral line shapes to appear broader and exhibit line shape distortions. In turn the electron density and temperature diagnostics are skewed. We discuss self-absorption of ground state aluminum transitions 394.4 and 396.15 nm, as well as ionic transitions at 281.6 and 464.3 nm. Saha-Boltzmann plots are used to evaluate the temperature from both neutral and ionic species. The self-absorption test is performed using a plane mirror to re-image the plasma prior to spectroscopic mapping. [1] D.M. Surmick and C.G. Parigger, \textit{J.Phys. B: Atom. Mol. Opt. Phys. }\textbf{48} (2015) 115701. [Preview Abstract] |
Thursday, November 19, 2015 11:12AM - 11:24AM |
B1.00002: Expansion dynamics and measurements of electron density distributions in laser-induced plasma Ghaneshwar Gautam, Christian Parigger Laser-induced micro-plasma is generated in a cell containing hydrogen gas of 99.999 purity at a pressure of 1.08 \texttimes 10$^{\mathrm{5}}$ Pa (810 Torr) by using Nd:YAG laser radiation at the wavelength of 1064 nm. The expansion dynamics are studied using the alpha and beta line shapes of the hydrogen Balmer series. Spatially and temporally resolved spectra are collected with a spectrometer-detector system. The recorded data are wavelength calibrated and detector-sensitivity corrected. Plasma dynamics at expansion speeds of the order of 1 to 10 km/s (Mach number 3 to 30) are of interest for early time delays after plasma generation. The Stark broadened spectral profiles of the hydrogen Balmer alpha line are used in the time delay range of 10 ns to 45 ns to determine plasma electron densities. For time delays of the order of 100 ns to 600 ns, the hydrogen Balmer beta is utilized as well to determine the electron density from the full-width at half-maximum and from the wavelength difference between the blue and red peaks. The experimental data are compared and fitted with computer simulated profiles that are available in the literature. In addition, the pure hydrogen results are compared with data obtained in laboratory air at standard ambient temperature and pressure [Preview Abstract] |
Thursday, November 19, 2015 11:24AM - 11:36AM |
B1.00003: Femtosecond laser machining of graphitic channels through diamond with dynamic aberration correction Brian K. Canfield, Lloyd M. Davis Diamond is a uniquely promising, radiation-hard substrate for high-energy particle detectors for next-generation particle tracking telescopes in the High Luminosity Large Hadron Collider. Synthetic polycrystalline diamonds of adequate area and thickness are available, but to overcome charge trapping at grain boundaries and crystal dislocation sites created by radiation damage, a 3D detector geometry comprised of an array of closely spaced internal columnar electrodes must be developed, rather than surface-mounted planar electrodes. We show that tightly focused femtosecond laser pulses can easily produce highly conductive graphitic electrodes on the surface of a diamond, but for creating internal electrodes, aberrations due to beam refraction on entering diamond (n$=$2.42) significantly enlarge the focal region. To correct aberrations and create a micron-sized focal region at variable depths, we have developed a lens system using a 0.68 NA aspheric lens and several other stock lenses with adjustable positions. Through LabVIEW, motorized actuators translate the lenses and diamond and trigger laser pulses. Beginning at the back, narrow columnar graphitic channels can be machined completely through 500 micron thick diamonds. Channel diameters vary with the energy and number of pulses. [Preview Abstract] |
Thursday, November 19, 2015 11:36AM - 11:48AM |
B1.00004: Cross sections for radiative electronic attachment to the molecules of astrophysical interest Marjan Khamesian, Nicolas Douguet, Maurice Raoult, Viatcheslav Kokoouline Several negative ions C$_n$H$^-$ ($n=4,6,8$) and C$_n$N$^-$ ($n=1,3,5$) have been recently observed in the interstellar medium (ISM). A possible mechanism of their formation is radiative electron attachment (REA). We have developed a first-principle theoretical approach to study REA applying it to the formation of the following negative molecular ions: CN$^-$, C$_2$H$^-$, C$_3$N$^-$, C$_5$N$^-$, C$_6$H$^-$, and C$_8$H$^-$. The theoretical approach is based on the UK R-matrix calculations. Cross sections and rate coefficients for formation of these ions by REA to the corresponding neutral radicals are calculated. There is no experimental data on REA of these ions. However, using a similar approach we have also calculated cross sections for photodetachment of the negative ions and compared the obtained results with available experimental data. The good agreement with photodetachment experimental data provides a confirmation that the REA cross sections obtained in this study are also reliable. The present study suggests that the studied negative ions are unlikely be formed by REA in the ISM. [Preview Abstract] |
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