Stark deceleration of molecular beams

The Stark decelerator for neutral polar molecules is the equivalent of a linear accelerator (LINAC) for charged particles, and exploits the interaction of a polar molecule with inhomogeneous time-varying electric fields. The deceleration (or acceleration) process can be seen as slicing a packet of molecules with a narrow velocity distribution out of the most intense part of the molecular beam pulse. This packet can then be decelerated or accelerated to any velocity, maintaining the narrow velocity distribution and the particle density in the packet.

photo1 photo2

A voltage difference of 40 kV is applied
to opposing electrodes.
(Photos: Ludwig Scharfenberg)

Each electrode of the decelerator is highly
polished to prevent high voltage breakdown

The Stark deceleration technique has been invented at the Radboud University Nijmegen in 1998 by Gerard Meijer and coworkers (now at the Fritz-Haber-Institut of the Max Planck Society in Berlin). The main components of our Stark decelerator have been constructed in Berlin, and transported to Nijmegen in September 2011.

Our decelerator is 2.6 meters long and consists of three decelerator modules of 105 electrode pairs each. The advantage of this long decelerator is that it allows us to accelerate or decelerate molecules using the so-called s=3 overtone mode. In this mode, every third electrode pair is used for acceleration/deceleration, while the intermediate pairs are used for transverse focusing.

A decelerator operating in this mode is ideally suited for scattering experiments: it combines a high efficiency with the ability to capture a large fraction of the molecular beam pulse. This results in a clear separation of the selected molecules from the remainder of the molecular beam pulse, independent of the selected final velocity.

Our recent publications on this topic:

Manipulation and control of molecular beams
Chemical Reviews 112, 4828-4878 (2012).

Operation of a Stark decelerator with optimum acceptance
Phys. Rev. A 79, 023410 (2009).

Taming molecular beams
Nature Physics 4, 595 (2008).

Transverse stability in a Stark decelerator
Phys. Rev. A 73, 023401 (2006).

Higher-order resonances in a Stark decelerator
Phys. Rev. A 71, 053409 (2005).