Events at Physics

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Events on Thursday, May 11th, 2023

Academic Calendar
Final exams
Abstract: *Note: actual end time may vary.* URL:
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Graduate Program Event
PhD Final Defense
New Approaches to Transverse NMR Gyroscopes
Time: 9:00 am - 11:00 am
Place: 5310 Chamberlin or
Speaker: Susan Sorensen, Physics Graduate Student
Abstract: In this thesis, I describe three approaches to the continuous operation of a transverse spin-exchange optically pumped NMR gyroscope. I demonstrate the simultaneous, continuous excitation of $^{131}$Xe and $^{129}$Xe using first modulations of the optical pumping (polarization modulation, PM), then using modulations of the applied bias field (pulse density modulation, PDM), and then using a combined approach that includes both polarization and field modulations (hybrid operation). I describe the theory behind the operation of the device, and the apparatus used to perform the experiments presented in this thesis. I then present results for each of the three operation modes - PM, PDM, and hybrid operation. For each, I give several key performance metrics, including linewidth, signal-to-noise ratio, field suppression factor, cross talk, angle-random walk, and bias instability. The field suppression factor and cross talk are unique metrics which have generally been ignored in this field of study. This thesis includes the best bias instability ever measured with this device, at $\sim$420~nHz. I close with a comparison of the three methods and a discussion of proposed future works.
Host: Thad Walker
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Gravitational Wave Science with Gamma Rays
Time: 2:30 pm - 3:30 pm
Place: CH4274/
Speaker: Matthew Kerr , US Naval Research Laboratory
Abstract: The Fermi Large Area Telescope (LAT) has now detected gamma-ray pulsations from over 100 millisecond pulsars, and its <300ns times tamping and nearly-unchanged experimental setup enable high-precision pulsar timing over its 15-year baseline. It is thus a "Gamma-ray Pulsar Timing Array" (PTA). Gamma rays are unaffected by propagation through the ionized interstellar medium, and the high-energy data thus enable the separation of propagation effects from the "spin noise" intrinsic to pulsars, perhaps arising from crustal superfluid turbulence. This capability in turns provides a clean measurement the correlated signals expected to be induced by nHz gravitational waves from merging supermassive black holes. I will compare this approach with radio PTAs and present recent results from the Gamma-ray PTA. In a second part, I will also present an overview and early results from Glowbug, a sensitive gamma-ray burst experiment built at NRL and recently launched to the International Space Station. Its large area and sensitive onboard burst detection algorithm will improve the odds of detecting short gamma-ray bursts associated with neutron star mergers, and its primary mission will completely overlap the O4 observing run of LIGO/Virgo/Kagra.
Host: Ke Fang
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