The Use of Molecular Beam Electric Resonance Technique for High Precision

Hyperfine Measurements

Charles McEachern, Ben McDonald

and Professor James Cederberg

Physics Department, St Olaf College, Northfield MN

The MolBeam Project

Our work observes pure hyperfine transitions in order to describe very precisely various electric and magnetic interactions in our molecules.

The Apparatus

“Old” is such an ugly word. We prefer to think of it as “aged to perfection.”

The Source

Our source is a metal tube with a small hole in it.

We use our effusive oven to vaporize our sample and send it out into the spectrometer.

The Lenses

We use electrostatic quadrupole lenses as state selectors. They focus the states we want into a path straight through the transition region.

How do the Lenses Work?

The lenses create an energy gradient that can be compared to a parabolic well.

Selecting States

To get a strong signal the lenses must select the appropriate velocity for a given state.

Transition Region

In this region there is an oscillating RF electric field and a DC field on large parallel plates. The combination of these two can induce a second order transition between hyperfine states.

Length of Transition Region

The long (about 2 meters) transition region increases the t of the transition, so the energy uncertainty is reduced.

More Lenses

These lenses are set identically to those just before the transition region.

They focus unchanged molecules to the detector.

Detector Transition Region Source

The Detector

Our detector is a tantalum filament. It has a high affinity for electrons, so it ionizes the molecules that hit it. We measure the current caused by these ionizations.

The Brains

Previous student researchers have written all of our software.

Simulating RunsWe can simulate the effects of various RF and DC voltages to pinpoint what we want our run to look like.

Effects of the RF and DC Voltage

The RF and DC fields change the shape of the data.

Data AnalysisOur collection software feeds us a scatter plot. We use Linefit to match a Rabi lineshape to our data very precisely.

Getting Results

Once we have fit many transitions, we can plug the numbers into a program called specfit.

This program gives us values for our constants. Ben will share what our numbers mean in the next talk.

Acknowledgements

I would like to thank Professor Cederberg, the St. Olaf College Physics Department, the Whittier endowment, and the Howard Hughes Medical Institute for their resources, funding, and the opportunity to participate in this research.