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B. E. Sauer

Publications and source records attributed to B. E. Sauer.

At least 55 records · Page 3Linked to original sources
arXiv2011

Stark deceleration of CaF molecules in strong- and weak-field seeking states

We report the Stark deceleration of CaF molecules in the strong-field seeking ground state and in a weak-field seeking component of a rotationally-excited state. We use two types of decelerator, a conventional Stark decelerator for the weak-field seekers, and an alternating gradient decelerator for the strong-field seekers, and we compare their relative merits. We also consider the application of laser cooling to increase the phase-space density of decelerated molecules.

physics.atom-ph↗
arXiv2011

Prospects for the measurement of the electron electric dipole moment using YbF

We discuss an experiment underway at Imperial College London to measure the permanent electric dipole moment (EDM) of the electron using a molecular beam of YbF. We describe the measurement method, which uses a combination of laser and radiofrequency resonance techniques to detect the spin precession of the YbF molecule in a strong electric field. We pay particular attention to the analysis scheme and explore some of the possible systematic effects which might mimic the EDM signal. Finally, we describe technical improvements which should increase the sensitivity by more than an order of magnitude over the current experimental limit.

physics.atom-ph↗
arXiv2011

Diffusion, thermalization and optical pumping of YbF molecules in a cold buffer gas cell

We produce YbF molecules with a density of 10^18 m^-3 using laser ablation inside a cryogenically-cooled cell filled with a helium buffer gas. Using absorption imaging and absorption spectroscopy we study the formation, diffusion, thermalization and optical pumping of the molecules. The absorption images show an initial rapid expansion of molecules away from the ablation target followed by a much slower diffusion to the cell walls. We study how the time constant for diffusion depends on the helium density and temperature, and obtain values for the YbF-He diffusion cross-section at two different temperatures. We measure the translational and rotational temperatures of the molecules as a function of time since formation, obtain the characteristic time constant for the molecules to thermalize with the cell walls, and elucidate the process responsible for limiting this thermalization rate. Finally, we make a detailed study of how the absorption of the probe laser saturates as its intensity increases, showing that the saturation intensity is proportional to the helium density. We use this to estimate collision rates and the density of molecules in the cell.

physics.atom-ph↗
arXiv2010

Prospects for measuring the electric dipole moment of the electron using electrically trapped polar molecules

Heavy polar molecules can be used to measure the electric dipole moment of the electron, which is a sensitive probe of physics beyond the Standard Model. The value is determined by measuring the precession of the molecule's spin in a plane perpendicular to an applied electric field. The longer this precession evolves coherently, the higher the precision of the measurement. For molecules in a trap, this coherence time could be very long indeed. We evaluate the sensitivity of an experiment where neutral molecules are trapped electrically, and compare this to an equivalent measurement in a molecular beam. We consider the use of a Stark decelerator to load the trap from a supersonic source, and calculate the deceleration efficiency for YbF molecules in both strong-field seeking and weak-field seeking states. With a 1s holding time in the trap, the statistical sensitivity could be ten times higher than it is in the beam experiment, and this could improve by a further factor of five if the trap can be loaded from a source of larger emittance. We study some effects due to field inhomogeneity in the trap and find that rotation of the electric field direction, leading to an inhomogeneous geometric phase shift, is the primary obstacle to a sensitive trap-based measurement.

physics.atom-ph↗
arXiv2009

Doppler-free laser spectroscopy of buffer gas cooled molecular radicals

We demonstrate Doppler-free saturated absorption spectroscopy of cold molecular radicals formed by laser ablation inside a cryogenic buffer gas cell. By lowering the temperature, congested regions of the spectrum can be simplified, and by using different temperatures for different regions of the spectrum a wide range of rotational states can be studied optimally. We use the technique to study the optical spectrum of YbF radicals with a resolution of 30 MHz, measuring the magnetic hyperfine parameters of the electronic ground state. The method is suitable for high resolution spectroscopy of a great variety of molecules at controlled temperature and pressure, and is particularly well-suited to those that are difficult to produce in the gas phase.

physics.atom-ph↗
arXiv2009

Transport of polar molecules by an alternating gradient guide

An alternating gradient electric guide provides a way to transport a wide variety of polar molecules, including those in high-field seeking states. We investigate the motion of polar molecules in such a guide by measuring the transmission of CaF molecules in their high-field seeking ground state, with the guide operating at a variety of switching frequencies and voltages. We model the guide using analytical and numerical techniques and compare the predictions of these models to the experimental results and to one another. The analytical results are approximate, but provide simple and useful estimates for the maximum phase-space acceptance of the guide and for the switching frequency required. The numerical methods provide more accurate results over the full range of switching frequencies. Our investigation shows that, even when the fields are static, some high-field seeking molecules are able to pass through the guide on metastable trajectories. We show that the maximum possible transmission requires accurate alignment within the guide and between the guide and detector.

physics.atom-ph↗
arXiv2008

Lifetime of the A(v'=0) state and Franck-Condon factor of the A-X(0-0) transition of CaF measured by the saturation of laser-induced fluorescence

We describe a method for determining the radiative decay properties of a molecule by studying the saturation of laser-induced fluorescence and the associated power broadening of spectral lines. The fluorescence saturates because the molecules decay to states that are not resonant with the laser. The amplitudes and widths of two hyperfine components of a spectral line are measured over a range of laser intensities and the results compared to a model of the laser-molecule interaction. Using this method we measure the lifetime of the A(v'=0) state of CaF to be tau=19.2 \pm 0.7 ns, and the Franck-Condon factor for the transition to the X(v=0) state to be Z=0.987 (+0.013 || -0.019). In addition, our analysis provides a measure of the hyperfine interval in the lowest-lying state of A(v'=0), Delta_e=4.8 \pm 1.1 MHz.

physics.atom-ph↗
arXiv2008

A robust floating nanoammeter

A circuit capable of measuring nanoampere currents while floating at voltages up to at least 25kV is described. The circuit relays its output to ground potential via an optical fiber. We particularly emphasize the design and construction techniques which allow robust operation in the presence of high voltage spikes and discharges.

physics.ins-det↗
arXiv2007

Pulsed beams as field probes for precision measurement

We describe a technique for mapping the spatial variation of static electric, static magnetic, and rf magnetic fields using a pulsed atomic or molecular beam. The method is demonstrated using a beam designed to measure the electric dipole moment of the electron. We present maps of the interaction region, showing sensitivity to (i) electric field variation of 1.5 V/cm at 3.3 kV/cm with a spatial resolution of 15 mm; (ii) magnetic field variation of 5 nT with 25 mm resolution; (iii) radio-frequency magnetic field amplitude with 15 mm resolution. This new diagnostic technique is very powerful in the context of high-precision atomic and molecular physics experiments, where pulsed beams have not hitherto found widespread application.

physics.atom-ph↗
arXiv2006

A supersonic beam of cold lithium hydride molecules

We have developed a source of cold LiH molecules for Stark deceleration and trapping experiments. Lithium metal is ablated from a solid target into a supersonically expanding carrier gas. The translational, rotational and vibrational temperatures are 0.9(0.1) K, 5.9(0.5) K and 468(17) K respectively. Although they have not reached thermal equilibrium with the carrier gas, we estimate that 90% of the LiH molecules are in the ground state, X^{1} Σ^{+} (v=0, J=0). With a single 7 ns ablation pulse, the number of molecules in the ground state is 4.5(1.8)*10^{7} molecules per steradian. A second, delayed, ablation pulse produces another LiH beam in a different part of the same gas pulse, thereby almost doubling the signal. A long pulse, lasting 150 microseconds, can make the beam up to 15 times more intense.

physics.atom-ph↗
arXiv2006

Probing the electron EDM with cold molecules

We present progress towards a new measurement of the electron electric dipole moment using a cold supersonic beam of YbF molecules. Data are currently being taken with a sensitivity of $10^{-27}\textrm{e.cm}/\sqrt{\textrm{day}}$. We therefore expect to make an improvement over the Tl experiment of Commins' group, which currently gives the most precise result. We discuss the systematic and statistical errors and comment on the future prospect of making a measurement at the level of $10^{-29}\textrm{e.cm}/\sqrt{\textrm{day}}$.

physics.atom-ph↗
arXiv2005

Bose-Einstein Condensation on a Permanent-Magnet Atom Chip

We have produced a Bose-Einstein condensate on a permanent-magnet atom chip based on periodically magnetized videotape. We observe the expansion and dynamics of the condensate in one of the microscopic waveguides close to the surface. The lifetime for atoms to remain trapped near this dielectric material is significantly longer than above a metal surface of the same thickness. These results illustrate the suitability of microscopic permanent-magnet structures for quantum-coherent preparation and manipulation of cold atoms.

cond-mat.other↗
arXiv2005

Stark shift of the $A^2Π_{1/2}$ state in $^{174}$YbF

We have measured the Stark shift of the $A^2Π_{1/2} - X^2Σ^+$ transition in YbF. We use a molecular beam triple resonance method, with two laser transitions acting as pump and probe, assisted by an rf transition that tags a single hyperfine transition of the X state. After subtracting the known ground state Stark shift, we obtain a value of $70.3(1.5) $Hz/(V/cm)$^2$ for the static electric polarizability of the state $A^2Π_{1/2}(J=1/2,f)$. From this we calculate a value $μ_e=2.46(3)$D for the electric dipole moment of the $A^2Π_{1/2}(v=0)$ state.

physics.atom-ph↗
arXiv2005

Cold atoms in videotape micro-traps

We describe an array of microscopic atom traps formed by a pattern of magnetisation on a piece of videotape. We describe the way in which cold atoms are loaded into one of these micro-traps and how the trapped atom cloud is used to explore the properties of the trap. Evaporative cooling in the micro-trap down to a temperature of 1 microkelvin allows us to probe the smoothness of the trapping potential and reveals some inhomogeneity produced by the magnetic film. We discuss future prospects for atom chips based on microscopic permanent-magnet structures.

physics.atom-ph↗
arXiv2005

Integrated optical components on atom chips

We report on the integration of small-scale optical components into silicon wafers for use in atom chips. We present an on-chip fibre-optic atom detection scheme that can probe clouds with small atom numbers. The fibres can also be used to generate microscopic dipole traps. We describe our most recent results with optical microcavities and show that single-atom detection can be realised on an atom chip. The key components have been fabricated by etching directly into the atom chip silicon substrate.

physics.atom-ph↗
arXiv2004

Micron-sized atom traps made from magneto-optical thin films

We have produced magnetic patterns suitable for trapping and manipulating neutral atoms on a $1 μ$m length scale. The required patterns are made in Co/Pt thin films on a silicon substrate, using the heat from a focussed laser beam to induce controlled domain reversal. In this way we draw lines and "paint" shaped areas of reversed magnetization with sub-micron resolution. These structures produce magnetic microtraps above the surface that are suitable for holding rubidium atoms with trap frequencies as high as ~1 MHz.

cond-mat.soft↗