Eric R. Hudson

Phase space manipulation of cold free radical oh molecules

We report bunching, slowing, and acceleration of a supersonically cooled beam of diatomic hydroxyl radicals (OH). In situ observation of laser-induced fluorescence along the beam propagation path allows for detailed characterization of longitudinal phase-space manipulation of OH molecules through the Stark effect by precisely sequenced inhomogeneous electric fields.

Production of cold formaldehyde molecules for study and control of chemical reaction dynamics with hydroxyl radicals

We propose a method for controlling a class of low temperature chemical reactions. Specifically, we show the hydrogen abstraction channel in the reaction of formaldehyde (H{sub 2}CO) and the hydroxyl radical (OH) can be controlled through either the molecular state or an external electric field. We also outline experiments for investigating and demonstrating control over this important reaction. To this end, we report the first Stark deceleration of H{sub 2}CO. We have decelerated a molecular beam of H{sub 2}CO essentially to rest, producing molecules at 100 mK with a density of {approx} 10{sup 6} cm{sup -3}.

Prospects for the cavity-assisted laser cooling of molecules

Cooling of molecules via free-space dissipative scattering of photons is thought not to be practicable due to the inherently large number of Raman loss channels available to molecules and the prohibitive expense of building multiple-repumping laser systems. The use of an optical cavity to enhance coherent Rayleigh scattering into a decaying cavity mode has been suggested as a potential method to mitigate Raman loss, thereby enabling the laser cooling of molecules to ultracold temperatures. We discuss the possibility of cavity-assisted laser cooling of particles without closed transitions, identify conditions necessary to achieve efficient cooling, and suggest solutions given experimental constraints. Specifically, it is shown that cooperativities much greater than unity are required for cooling without loss, and that this could be achieved via the superradiant scattering associated with intracavity self-localization of the molecules. Particular emphasis is given to the polar hydroxyl radical (OH), cold samples of which are readily obtained from Stark deceleration.

OH hyperfine ground state : From precision measurement to molecular qubits

We perform precision microwave spectroscopy--aided by Stark deceleration--to reveal the low-magnetic-field behavior of OH in its {sup 2}{pi}{sub 3/2} rovibronic ground state, identifying two field-insensitive hyperfine transitions suitable as qubits and determining a differential Lande g factor of 1.267(5)x10{sup -3} between opposite-parity components of the {lambda} doublet. The data are successfully modeled with an effective hyperfine Zeeman Hamiltonian, which we use to make a tenfold improvement of the magnetically sensitive, astrophysically important {delta}F={+-}1 satellite-line frequencies, yielding 1 720 529 887(10) Hz and 1 612 230 825(15) Hz.

Cold free-radical molecules in the laboratory frame

A special class of molecules that are important to many subfields in molecular dynamics and chemical physics, namely free-radical molecules, now enjoy a significant degree of center-of-mass motion control in the laboratory frame. The example reported in this paper concerns the hydroxyl radical (OH), which, after the internal degrees of freedom are cooled in a supersonic expansion, has been bunched, accelerated, and slowed using time-varying inhomogeneous electric fields. In situ observations of laser-induced fluorescence along the beam propagation path allows for detailed characterization of the longitudinal phase-space manipulation of OH molecules by the electric fields. The creation of a pulse containing 10{sup 3}-10{sup 6} molecules possessing a longitudinal velocity spread from 2 to 80 m/s around a mean laboratory velocity variable from 550 m/s to rest with only a few mm spatial extent represents an exciting and useful experimental capability for exploring free-radical dynamics.

Mitigation of loss within a molecular Stark decelerator

Abstract.The transverse motion inside a Stark decelerator plays a large role in the total efficiency of deceleration. We differentiate between two separate regimes of molecule loss during the slowing process. The first mechanism involves distributed loss due to coupling of transverse and longitudinal motion, while the second is a result of the rapid decrease of the molecular velocity within the final few stages. In this work, we describe these effects and present means for overcoming them. Solutions based on modified switching time sequences with the existing decelerator geometry lead to a large gain of stable molecules in the intermediate velocity regime, but fail to address the loss at very low final velocities. We propose a new decelerator design, the quadrupole-guiding decelerator, which eliminates distributed loss due to transverse/longitudinal couplings throughout the slowing process and also exhibits gain over normal deceleration to the lowest velocities.

Efficient Stark deceleration of cold polar molecules

Abstract.Stark deceleration has been utilized for slowing and trapping several species of neutral, ground-state polar molecules generated in a supersonic beam expansion. Due to the finite physical dimension of the electrode array and practical limitations of the applicable electric fields, only molecules within a specific range of velocities and positions can be efficiently slowed and trapped. These constraints result in a restricted phase space acceptance of the decelerator in directions both transverse and parallel to the molecular beam axis; hence, careful modeling is required for understanding and achieving efficient Stark decelerator operation. We present work on slowing of the hydroxyl radical (OH) elucidating the physics controlling the evolution of the molecular phase space packets both with experimental results and model calculations. From these results we deduce experimental conditions necessary for efficient operation of a Stark decelerator.

Precision Measurement Based on Ultracold Atoms and Cold Molecules

We report our group’s recent research efforts on precision test of fundamental physics using ultracold atoms and cold molecules.

Cold free radical molecules in the laboratory frame

We report manipulation of a supersonically-cooled beam of diatomic hydroxyl radicals by precisely-sequenced inhomogeneous electric fields. In-situ observation of laser-induced fluorescence along the beam path allows for observation of longitudinal phase-space evolution.