Our research uses supersonic expansion coupled with Stark deceleration to cool and slow polar molecules. We start by expanding a mixture of Krypton and the molecule of interest through  a small aperture into our vacuum system. The resulting pulse of ground-state molecules has a narrow velocity distribution in three dimensions and a mean longitudinal velocity of several hundred meters per second.

The next step is to slow the molecules into the rest frame of the laboratory. After the expansion, the molecular pulse propagates through a skimmer, which allows for differential pumping between vacuum chambers. The molecules then fly into the entrance of the Stark decelerator. The geometry of the electrodes that make up the decelerator, creates a maximum of electric field in the longitudinal direction directly between an electrode pair. As the molecules propagate into this increasing electric field they lose longitudinal kinetic energy. If the molecules were allowed to continue down the potential hill they would regain the lost kinetic energy; however, before they begin to accelerate, the electric field is instantaneously turned off, thus removing energy from the molecules. This process is repeated with successive stages of electrodes until the molecules have been sufficiently slowed to be loaded into a magnetic trap. Additionally, transverse guidance of the molecules is achieved because the molecules are attracted to the minimum of electric field along the center of the decelerator. Successive electrode pairs are orientated orthogonally to one another to guide the molecules equally in both transverse dimensions.

Once the molecules have been slowed to near zero velocity, they can be trapped by either static magnetic or electric fields. We currently trap ammonia molecules in an electrostatic trap formed by four electrodes. We use Monte Carlo simulations to optimize the trap loading timing. An example of loading the electric trap can be seen in the following simulations. (Phase space) (Coordinate space)

In addition to trapped molecule experiments, we use the Stark decelerator to provide molecular beams with controllable mean velocities. In these experiments, we can vary the collision energy between the reactants and thus tune over collision channel thresholds. Recently, we developed a new slowing protocol that greatly reduces the velocity spread of a velocity tuned molecular beam thus allowing for more precise measurements of thresholds and collision resonances. (See Figure below.)