Bulletin of the American Physical Society
2017 Fall Meeting of the APS New England Section
Volume 62, Number 15
Friday–Saturday, October 20–21, 2017; Kingston, Rhode Island
Session E2: Optics and Astrophysics |
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Saturday, October 21, 2017 8:30AM - 8:45AM |
E2.00001: Magneto-Optical Trap Thermometry Using a Triggered Electro-Optic Modulator S.A. Entner, J. M. Kwolek, D.S. Goodman, W.W. Smith Magneto-optical trapping and cooling is fundamental to the study of ultra-cold gases, often serving as the workhorse for many cutting-edge, cold-atomic-physics applications. The magneto-optical trap creates a cold ($\sim$ 100 uK) localized cloud of neutral atoms, therefore, characterizing the temperature of the cloud is an essential task. Our poster will describe the implementation of a modified release-and-recapture technique that measures a trapped sodium cloud’s temperature via spatiotemporal fluorescence imaging (STFI). The technique uses a triggered electro-optic modulator and CCD camera to release, recapture, and image the ballistic expansion of the atom-cloud. Ultimately, tracking the cloud’s expansion allows us to determine the temperature of the trapped atom-cloud. [Preview Abstract] |
Saturday, October 21, 2017 8:45AM - 9:00AM |
E2.00002: Testing Parameterized Theories of General Relativity using Gravitational Waves Radha Mastandrea, Alan Weinstein The recent detections of gravitational waves (GWs) by the Laser Interferometer Gravitational-Wave Observatory (LIGO) have provided researchers with the first opportunities to test general relativity (GR) in the strong-field and highly-dynamical limit. Qualitative tests of the agreement between LIGO's GW observations and classical GR have already been done; we have carried out more quantitative tests in terms of controlled, parameterized deviations from GR. In this project, we simulate a number of binary black hole (BBH) merger waveforms with known amplitude and phase deviations from those predicted by GR that are governed by the real and imaginary parts, respectively, of a complex parameter $\lambda$. We use Bayesian analysis to recover the deviation. We then provide an estimate of the number of GW detections from BBH mergers that are necessary to establish a given deviation from classical GR, notably finding that under 80 events are necessary to determine $\lambda$ to a precision of 0.025 (a fractional precision of 5\% for $\lambda=0.5$). [Preview Abstract] |
Saturday, October 21, 2017 9:00AM - 9:15AM |
E2.00003: By Parallax to the Moon: An exercise with online data Charles H. Holbrow On May 23, 2007 at 16:09:31 UTC, Peter Lawrence at Selsey, UK (50.73502\mbox{$^{\circ}$}~N, 0.78977\mbox{$^{\circ}$}~W), and Anthony Ayiomamitis at Athens, Greece (37\mbox{$^{\circ}$}~59$'$~2.3$''$~N, 23\mbox{$^{\circ}$}~43$'$~40.1$''$~E), photographed the Moon as it passed close to the bright star Regulus ($\alpha$-Leonis).\footnote{\url{http://www.etwright.org/astro/moonpar.html}} Their two pictures show the Moon at different angular separations from Regulus because of parallax of the Moon relative to this much more distant star. You can extract from the pictures the parallax angle of 1118$''$ and use it to find the distance from Earth to Moon. However, you can not use the simplifying assumptions that are standard in astronomy texts because the triangle formed by the locations of Selsey, Athens, and the Moon is oblique; no two of its sides are equal; and it lies in a plane tilted relative to the horizontal planes of the observers in a way not easy to visualize. I will show how a student can set up the problem in terms of vectors, evade difficulties of three dimensional visualization, and obtain a value of the Earth-Moon distance on that day and at that time of $373,000 \pm 4,000$~km in good agreement with its actual value. [Preview Abstract] |
Saturday, October 21, 2017 9:15AM - 9:30AM |
E2.00004: Two-dimensional (2D) semiconductor: Probing by femtosecond broadband continuum second harmonic generation (SHG) measurement Mohammad Mokim, Feruz Ganikhanov After the remarkable success of graphene, two-dimensional (2D) semiconductors have recently become the focus of fundamental research due to their novel electronic and optical properties, making for very promising applications in nano- and optoelectronic devices. We demonstrate an effective microspectroscopy technique by tracing the dispersion of second order nonlinear susceptibility $\chi^{\mathrm{(2)}}$ to characterize the monolayer tungsten diselenide (WSe$_{\mathrm{2}})$ within the photon energy range of 2.4-3.2 eV. We then retrieve, with reasonable precision, the fundamental bandgap and exciton binding energy of this semiconductor. To perform the experiment, ultra-broadband continuum pulses served as the fundamental beam while its second harmonic spectrum in visible and ultraviolet (UV) was detected and analyzed with better than 0.3 nm spectral resolution (\textless 2 meV). In this presentation, I will discuss our recently obtained experimental results that can be crucial to refining the theoretical calculations. [Preview Abstract] |
Saturday, October 21, 2017 9:30AM - 9:45AM |
E2.00005: Sensitive photoacoustic trace gas detection with a moving optical grating Wenyu Bai, Lian Xiong, Feifei Chen, Fapeng Yu, Xian Zhao, Gerald Diebold Examination of the wave equation for the photoacoustic effect shows that photoacoustic waves can be excited by steady motion of a heating source. Compared with the traditional excitation methods such as the pulsed or amplitude-modulated laser excitation, photoacoustic waves launched by moving sources permits greater sound controllability, higher input radiation energy, and most importantly, the possibility of achieving optimal optical to acoustic energy conversion efficiency. In this talk, we first show that in the linear acoustic regime when a laser source moves at the sound speed in a one-dimensional geometry, the amplitude of the acoustic wave grows linearly in time without bound. Second, use of this principle is described for trace detection of gases using two frequency shifted beams from a CO$_{2}$ laser directed at an angle to each other to give optical fringes that move at the sound speed in a cavity with a longitudinal resonance. The photoacoustic signal is detected with a high $Q$, piezoelectric crystal with a resonance on the order of $443$ kHz. As the grating frequency, the length of the resonator, and the crystal must all have matched frequencies, three resonances are used to advantage to produce sensitivity that extends to the parts-per-quadrillion level. [Preview Abstract] |
Saturday, October 21, 2017 9:45AM - 10:00AM |
E2.00006: Sub-picometer Laser Distance Gauge for Gravitational and Astronomical Instruments James D. Phillips, Dan Kaplan, Robert D. Reasenberg, Tom Roberts The Tracking Frequency laser Gauge (TFG) can measure distances in the range 0.01-1000 m. We have demonstrated accuracy of 2 picometers (pm, 10\textasciicircum -12 m) in 1 s, and 40 femtometers (fm, 10\textasciicircum -15 m) in 30 s when using a resonant measurement interferometer with a finesse of 130. It is the world's most accurate laser distance gauge. The TFG can be the sensor for new tests of the equivalence principle, including a test with antimuons; and for optical trusses in demanding spaceborne astronomical instruments, such as telescopes with exoplanet coronagraphs and others using segmented or distributed apertures. The TFG locks a laser to the measurement interferometer. This architecture gives it substantial advantages over the traditional precision instrument, the heterodyne phase gauge (HPG). The TFG is free of an important source of cyclic bias that limits the HPG accuracy. The TFG's readout is a radio frequency derived from an optical heterodyne, not an RF phase as in the HPG. The TFG measures absolute distance (to $\mu $m precision) with little or no additional hardware. The TFG is now operating at the Illinois Institute of Technology (IIT), where we are refining and testing error models to increase reliability and improve accuracy. [Preview Abstract] |
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