Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 62, Number 17
Friday–Saturday, October 20–21, 2017; Fort Collins, CO
Session L1: Atomic, Molecular and Optical Physics IV |
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Chair: Jason Jones, University of Arizona Room: Lory Student Center 372 |
Saturday, October 21, 2017 11:10AM - 11:22AM |
L1.00001: Understanding the angular momentum of light in the presence of structured darkness Samuel Alperin, Mark Siemens It is well known that passing a Gaussian beam through a 2$\pi $m helical phase optic imparts the beam with an orbital angular momentum (OAM) of m$\hbar $ when m is an integer. However, this linear relationship between the topological charge of the generating phase optic and the OAM of the generated beam does not in general hold for non-integer m. We explain this apparent discrepancy between the topology of the optic and the OAM of the generated mode. First, we show that the fundamental action of a spiral phase optic is to impart the transmitted beam with m$\hbar $ of intrinsic OAM, the component of the OAM that is invariant on translation. We then investigate the structure and origin of the other component of the fractional vortex mode, the extrinsic AM carrying component which we call structured darkness. It is shown that the structured darkness found in fractional vortex beams is the effect of evanescent structure at the surface of the phase optic upon the propagating mode. It is concluded that the extrinsic angular momentum of fractional vortex beams, as well as their rich topological structure, can be explained by the form of the evanescent structure at the surface of the associated phase optic. [Preview Abstract] |
Saturday, October 21, 2017 11:22AM - 11:34AM |
L1.00002: Spin to Orbital Angular Momentum Conversion Through Second Harmonic Generation in Underdense Plasmas Alex Wilhelm, Randy Lemons, David Schmidt, Charles Durfee Second harmonic generation (SHG) is forbidden in an isotropic medium, so non-centrosymmetric optical crystals are used for efficient frequency conversion. However, SHG light can also be generated in an isotropic underdense plasma by driving a nonlinear polarization where the symmetry is broken by a gradient in the plasma density or laser intensity. In this presentation, we demonstrate that in this SHG process spin angular momentum of a circularly polarized photon is converted to orbital angular momentum (OAM) of the output circularly polarized photon. This principle can be extended to generating second harmonic OAM beams of arbitrary vortex phase by mixing the spin and OAM states of the fundamental. To our knowledge this is the first demonstrated case of conversion of optical spin to a beam with OAM in an isotropic medium. [Preview Abstract] |
Saturday, October 21, 2017 11:34AM - 11:46AM |
L1.00003: A Joule-class, 0.5 kHz repetition rate picosecond diode-pumped laser Cory Baumgarten, Michael Pedicone, Herman Bravo, Hanchen Wang, Liang Yin, Carmen Menoni, Jorge Rocca, Brendan Reagan Joule level, high repetition rate laser systems enable a number of applications in which simultaneously high pulse energy and average power are required. These applications include the generation of high average power soft x-ray lasers, optical parametric chirp pulse amplifier sources of very short duration pulses, generation of bright, coherent and incoherent pulses of extreme ultraviolet, soft x-ray, and hard x-ray radiation. We report on the development of an entirely diode-pumped chirped pulse amplification laser system that produces pulses with up to 1.5 J pulse energy at repetition rates up to 500 Hz (750 W average power) which can be compressed resulting in the production of Joule-level, 5 ps duration pulses. The main amplifier is based on cryogenically-cooled Yb:YAG active mirrors. The laser produces pulses with good beam quality, and its stable operation is demonstrated. The system is quite compact, occupying an optical table area of only 4.5 m$^{\mathrm{2}}$, making it an ideal source for tabletop experiments. [Preview Abstract] |
Saturday, October 21, 2017 11:46AM - 11:58AM |
L1.00004: Ultrastable silicon cavity at 4 K using a continuously-operating closed-cycle cryostat Lindsay Sonderhouse, Wei Zhang, John Robinson, Eric Oelker, Craig Benko, John Hall, Thomas Legero, Dan Matei, Fritz Riehle, Uwe Sterr, Jun Ye Ongoing advances in ultrastable lasers drive further development of the optical atomic clock. Currently, the most stable lasers are based on silicon cavities that are cooled to 124 K. The stability of these lasers is limited by the composite thermal noise of the coatings, substrates, and spacer. To further improve the stability of these lasers to a level comparable to the natural linewidth of state-of-the-art clock transitions, silicon cavities will need to be cooled to lower temperatures. Two major obstacles to operating at low temperatures are the vibration noise and temperature fluctuations of the closed-cycle cryostat, which can produce noise substantially above the thermal noise floor. We overcome these limitations with a custom-designed cryostat that cools the cavity to 4 K while simultaneously suppressing temperature fluctuations and vibration noise below the thermal noise floor of $6 \times 10^{-17}$. The closed-cycle cryostat also offers continuous cooling, removing the need for cryogen refilling. We demonstrate a $1 \times 10^{-16}$ stability from .06 to 100 s and a linewidth of 17 mHz at 1542 nm. This represents a tenfold improvement in short-term stability and a $10^4$ improvement in linewidth over past low-temperature results. [Preview Abstract] |
(Author Not Attending)
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L1.00005: Highly Excited States of Chlorine Substituted Polyatomic Molecules in the Vacuum-Ultraviolet Quynh Nguyen, William Peters, Ryan Fortenberry, Margaret Murnane, Henry Kapteyn Electronic states up to the vacuum-UV range and ionization potentials of the chlorine-substituted cumuleneone series are computed with the coupled cluster methods in order to explore the valence and Rydberg properties of lone-pair terminated, $\pi $-conjugated systems in potential resonance with lone pairs from elsewhere in the system. The carbon chain elongation within the family, ClHCnO, influences the electronic excitations, characters, and ionization potentials. Comparison between the hydrocarbons and the corresponding chlorinated derivatives give notable similarities. An increase of Rydberg mixing with valence character is observed, which causes these highly energetic states to be more diffuse and hence, more challenging to study. Thus, we explore the effects of diffuse basis functions to accurately predict the photophysical properties of the systems. Future implications for sub-fs ultrafast dynamics in highly excited states of polyatomic molecules will be discussed. [Preview Abstract] |
Saturday, October 21, 2017 12:10PM - 12:22PM |
L1.00006: Cavity enhanced high power 243 nm CW laser for two-photon laser cooling of hydrogen. Zakary Burkley, Samuel Cooper, Cory Rasor, Adam Brandt, Dylan Yost High power 243 nm CW laser sources have long enabled spectroscopic studies of atomic hydrogen through excitation of the 1S-2S 2-photon transition. With sufficient power, such lasers could also allow for two-photon laser cooling of hydrogen. In this talk, we present a 243 nm laser system with 750 mW of average power. We couple this radiation to a simple linear optical cavity and obtain 30 W of intracavity power. This power level is sufficient for one-dimensional laser cooling if it can be overlapped with a cryogenic beam of magnetically guided atomic hydrogen. [Preview Abstract] |
Saturday, October 21, 2017 12:22PM - 12:34PM |
L1.00007: Robust Simulation of Neutral Atom Trapping for Minimal Degree of Freedom Mixing Yonge Lange Simmons, Samuel Cooper, Adam Brandt, Zak Burkley, Cory Rasor, Dylan Yost Laser cooling is a strong candidate for decreasing systematic error in precision spectroscopy of hydrogen. This talk outlines a method for simulating neutral atoms in magnetic traps, guides, and lenses for validating designs for confining atomic hydrogen and reducing degree of freedom mixing during laser cooling. Our simulation method takes advantage of two techniques. The first being accuracy of boundary element analysis (ESRF's Radia) to calculate permanent magnet and current source magnetic fields. The second is the computational speed of numerical methods including interpolation and a symplectic integrator. The later of which performs well in energy conservation, which is ideal for determining the degree of freedom mixing over long time scales in a neutral atom trap.\\ [Preview Abstract] |
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