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.