Bulletin of the American Physical Society
2016 Annual Meeting of the APS Mid-Atlantic Section
Volume 61, Number 16
Saturday–Sunday, October 15–16, 2016; Newark, Delaware
Session G3: Optical Science II |
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Chair: Siyu Luo, University of Delaware Room: Sharp Laboratory 131 |
Sunday, October 16, 2016 1:30PM - 2:06PM |
G3.00001: Waveform-controlled High Harmonics From Plasmas Invited Speaker: Julia Mikhailova . [Preview Abstract] |
Sunday, October 16, 2016 2:06PM - 2:18PM |
G3.00002: Excited State Vibrational Dynamics of a Porphyrin Molecule Measured with Multidimensional Pump-Degenerate Four-Wave Mixing Spectroscopy Baxter Abraham, Jesus Nieto-Pescador, Lars Gundlach Knowledge of the excited state relaxation mechanisms of porphyrin molecules is necessary for understanding the underlying photochemical processes of many biological and artificial light harvesting systems. The complex electronic structure of these molecules has given rise to several conflicting relaxation models. We employ pump-degenerate four-wave mixing spectroscopy to provide further insight into the ultrafast dynamics. An actinic pump pulse precedes a three pulse probing sequence which produces a spatially independent pulse induced by polarization changes in the excited state. Recording the intensity of the generated pulse over the course of increasing pump delays produces a time-varying signal that is Fourier transformed to observe time-dependent frequency spectra. Measurements on a porphyrin archetype reveal new information on the vibrational dynamics of the excited state. Raman active features are monitored after photoexcitation, and amplitude and energy changes are observed. Peaks attributed to the chromophore are in phase with each other and out of phase with solvation shell vibrations. Measured frequency upshifts are consistent with relaxation in an anharmonic potential energy surface. These results elucidate the role of vibrational cooling versus optically dark states. [Preview Abstract] |
Sunday, October 16, 2016 2:18PM - 2:30PM |
G3.00003: Substitution effects in strong and ultrastrong field ionization of chlorinated methane Patrick Grugan, Siyu Luo, Sam Hughes, Ryan Welch, Barry Walker Intensity dependent yields of carbon and chlorine ion fragments from chlorinated methane species are studied in strong and ultrastrong laser fields. Comparison to carbon ion fragments from methane under similar conditions shows no difference in the ion yields for chloromethane. Methane derived carbon ions display no anisotropy with respect to the laser polarization direction where chloromethane has little or no anisotropy, within the standard of error for our spectrometer. The energy distributions of carbon and chlorine ions are also collected and it is shown that the fragment energy of the highest charge states of carbon can reach energies of 20 eV to 40 eV for C$^{3+}$ and C$^{4+}$ respectively. A previous study of the intensity dependence of carbon ions from methane\footnote{S.Palaniyappan et. al., Phys. Rev. Lett. \textbf{100},183001(2008)} , showed that production of the lowest charge states of carbon, C$^{+}$ and C$^{2+}$ are heavily influenced by molecular ionization effects and that the highest charge states of carbon, C$^{5+}$, show no molecular dependence in its production. The current work details a similar result for the chlorinated methane series. [Preview Abstract] |
Sunday, October 16, 2016 2:30PM - 3:06PM |
G3.00004: Generation of high-power terahertz radiation and its interaction with matter Invited Speaker: Ki-Yong Kim Sandwiched between the optical and microwave regimes, the far infrared or terahertz (THz) frequency range has recently drawn special attention due to its ubiquitous nature and broad applications. THz radiation (or T-rays) can easily pass through non-polar materials such as clothing, paper, plastics, wood and ceramics. This property allows many applications in molecular sensing, biomedical imaging and spectroscopy, security scanners, and plasma diagnostics. High-power THz generation is also vital for applications in nonlinear THz optics and spectroscopy, and so there is a growing demand for intense, compact THz sources. Here I will talk about our approach in using tabletop, ultrashort-pulsed lasers to produce intense THz radiation and study nonlinearities driven by THz pulses in matter. Recently, we have demonstrated strong THz field generation via cylindrical focusing of two-color laser pulses in air. In this experiment, a terawatt (TW) laser pulse at 800 nm passes through a nonlinear crystal (BBO) and generates its second harmonic pulse at 400 nm. Both pulses pass through a cylindrical lens and are focused together to generate a 2-dimensional plasma sheet in air. This plasma sheet can yield scalable THz radiation approaching gigawatt (GW) peak power. Such an intense THz pulse can be used to accelerate electrons at relativistic velocities and to study quasi-DC tunneling ionization of atoms and molecules at THz frequencies. [Preview Abstract] |
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