PROBING BUFFER-GAS COOLED MOLECULES WITH DIRECT FREQUENCY COMB SPECTROSCOPY IN THE MID-INFRRARED

We present the first demonstration of cavity-enhanced direct frequency comb spectroscopyfootnote{A. Foltynowicz emph{et al}. Cavity-enhanced optical frequency comb spectroscopy in the mid-infrared application to trace detection of hydrogen peroxide. Applied Physics B, vol. 110, pp. 163�175, 2013.} on buffer-gas cooled moleculesfootnote{D. Patterson and J. M. Doyle. Cooling molecules in a cell for FTMW spectroscopy. Molecular Physics 110, 1757�1766, 2012.}. By coupling a mid-infrared frequency comb to a high-finesse cavity surrounding a helium buffer-gas chamber, we can gather rotationally resolved absorption spectra with high sensitivity over a broad wavelength region. The measured $sim$10 K rotational and translational temperatures of buffer-gas cooled molecules drastically simplify the observed spectra, compared to those of room temperature molecules, and allow for high spectral resolution limited only by Doppler broadening (10-100 MHz). Our system allows for the extension of high-resolution spectroscopy to larger molecules, enabling detailed analysis of molecular structure and dynamics, while taking full advantage of the powerful optical properties of frequency combs

A Ten-Fold Improvement to the Limit of the Electron Electric Dipole Moment

The Standard Model of particle physics is wonderfully successful in its predictions but known to be incomplete. It fails to explain the existence of dark matter, and the fact that a universe made of matter survived annihilation with antimatter following the big bang. Extensions to the Standard Model, such as weak-scale Supersymmetry, provide explanations for some of these phenomena by asserting the existence of new particles and new interactions that break symmetry under time-reversal. These theories predict a small, yet potentially measurable electron electric dipole moment (EDM), $d_e$, that also violates time-reversal symmetry. Here, we report a new measurement of the electron EDM in the polar molecule thorium monoxide (ThO): $d_e = -2.1 \pm 3.7stat \pm 2.5syst x 10-29$ e cm, which corresponds to an upper limit of $|d_e| <8.7 x 10-29$ e cm with 90 \% confidence. This is more than an order of magnitude improvement in sensitivity compared to the previous limit. This result sets strong constraints on new physics at an energy scale (TeV) at least as high as that directly probed by the Large Hadron Collider. The unprecedented precision of this EDM measurement was achieved by using the high effective electric field within ThO to greatly magnify the EDM signal. Valence electrons travel relativistically near the heavy thorium nucleus and experience an effective electric field of about 100 GV/cm, millions of times larger than any static laboratory field. The reported measurement is a combination of millions of separate EDM measurements performed with billions of ThO molecules in a cold, slow buffer gas beam. Other features of ThO, such as a near-zero magnetic moment and high electric polarizability, allow potential systematic errors to be drastically suppressed and ensure the accuracy of our measurement.Physic

Hydrothermal plume dynamics on Europa : implications for chaos formation

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): E03008, doi:10.1029/2003JE002073.Hydrothermal plumes may be responsible for transmitting radiogenic or tidally generated heat from Europa's rocky interior through a liquid ocean to the base of its ice shell. This process has been implicated in the formation of chaos regions and lenticulae by melting or exciting convection in the ice layer. In contrast to earlier work, we argue that Europa's ocean should be treated as an unstratified fluid. We have adapted and expanded upon existing work describing buoyant plumes in a rotating, unstratified environment. We discuss the scaling laws governing the flow and geometry of plumes on Europa and perform a laboratory experiment to obtain scaling constants and to visualize plume behavior in a Europa-like parameter regime. We predict that hydrothermal plumes on Europa are of a lateral scale (at least 25–50 km) comparable to large chaos regions; they are too broad to be responsible for the formation of individual lenticulae. Plume heat fluxes (0.1–10 W/m2) are too weak to allow complete melt-through of the ice layer. Current speeds in the plume (3–8 mm/s) are much slower than indicated by previous studies. The observed movement of ice blocks in the Conamara Chaos region is unlikely to be driven by such weak flow

Shot-noise-limited spin measurements in a pulsed molecular beam

Heavy diatomic molecules have been identified as good candidates for use in electron electric dipole moment (eEDM) searches. Suitable molecular species can be produced in pulsed beams, but with a total flux and/or temporal evolution that varies significantly from pulse to pulse. These variations can degrade the experimental sensitivity to changes in spin precession phase of an electri- cally polarized state, which is the observable of interest for an eEDM measurement. We present two methods for measurement of the phase that provide immunity to beam temporal variations, and make it possible to reach shot-noise-limited sensitivity. Each method employs rapid projection of the spin state onto both components of an orthonormal basis. We demonstrate both methods using the eEDM-sensitive H state of thorium monoxide (ThO), and use one of them to measure the magnetic moment of this state with increased accuracy relative to previous determinations.Comment: 12 pages, 6 figure

Magnetic and electric dipole moments of the H 3Δ1H\ {}^3\Delta_1 state in ThO

The metastable $H \ {}^3\Delta_1$ state in the thorium monoxide (ThO) molecule is highly sensitive to the presence of a CP-violating permanent electric dipole moment of the electron (eEDM). The magnetic dipole moment $\mu_H$ and the molecule-fixed electric dipole moment $D_H$ of this state are measured in preparation for a search for the eEDM. The small magnetic moment $\mu_H = 8.5(5) \times 10^{-3} \ \mu_B$ displays the predicted cancellation of spin and orbital contributions in a ${}^3 \Delta_1$ paramagnetic molecular state, providing a significant advantage for the suppression of magnetic field noise and related systematic effects in the eEDM search. In addition, the induced electric dipole moment is shown to be fully saturated in very modest electric fields ($<$ 10 V/cm). This feature is favorable for the suppression of many other potential systematic errors in the ThO eEDM search experiment.Comment: 4 pages, 3 figure

Thrust Stand for Electric Propulsion Performance Evaluation

An electric propulsion thrust stand capable of supporting testing of thrusters having a total mass of up to 125 kg and producing thrust levels between 100 microN to 1 N has been developed and tested. The design features a conventional hanging pendulum arm attached to a balance mechanism that converts horizontal deflections produced by the operating thruster into amplified vertical motion of a secondary arm. The level of amplification is changed through adjustment of the location of one of the pivot points linking the system. Response of the system depends on the relative magnitudes of the restoring moments applied by the displaced thruster mass and the twisting torsional pivots connecting the members of the balance mechanism. Displacement is measured using a non-contact, optical linear gap displacement transducer and balance oscillatory motion is attenuated using a passive, eddy-current damper. The thrust stand employs an automated leveling and thermal control system. Pools of liquid gallium are used to deliver power to the thruster without using solid wire connections, which can exert undesirable time-varying forces on the balance. These systems serve to eliminate sources of zero-drift that can occur as the stand thermally or mechanically shifts during the course of an experiment. An in-situ calibration rig allows for steady-state calibration before, during and after thruster operation. Thrust measurements were carried out on a cylindrical Hall thruster that produces mN-level thrust. The measurements were very repeatable, producing results that compare favorably with previously published performance data, but with considerably smaller uncertainty