Electron scattering & high resolution spectroscopy from cold atoms in an AC-MOT

Robin Kaiser

Matthew Harvey, Andrew James Murray, John Chidowerem Agomuo

Electron scattering from cold atoms provides significant advantages compared to collisions with atoms emanating from a hot effusive source. Here we describe a new type of cold atom trap (the AC-MOT) that allows measurements from cold and trapped atoms at low impact energies, by eliminating the MOT magnetic fields very rapidly. The design and operation of the AC-MOT will be described, together with results from experiments that have been performed.

Robin Kaiser

Michael E. Jones

This thesis presents details of a new type of cold atom electron source (CAES) that uses an alternating current magneto-optical trap (AC-MOT). Cold atom electron sources produce electron bunches by threshold photoionisation from a population of laser-cooled atoms. The electrons extracted from the atoms are made into a beam which has an ultra-low transverse velocity distribution. The low velocity distribution increases the brightness and reduces the energy spread of the beam, making CAESs potential sources for future electron diffraction and electron spectroscopy studies. The newly commissioned source detailed here produces focused electron bunches with characteristic temperatures as low as 12.6 ± 0.8 K, at a rate of up to 10 Hz, and with a bunch charge of 2.2±0.2fC, comparable to other state-of-the-art cold atom electron sources. The AC-MOT CAES can also produce cold bunches with energies <200 eV, which is lower than has previously been reported for this type of source. The electrons originate from a population of laser-cooled 85Rb atoms held in an AC- MOT. The AC-MOT CAES design allows the magnetic trapping fields to be switched to zero in 32 μs, more than �ˆ�175 times faster than is possible using a comparable DC-MOT source. This means that electron bunches can be created and extracted in a magnetic field-free environment without any reduction in trap density and hence bunch charge, as occurs in conventional DC-MOT sources. The design, development, characterisation, and operation of the systems needed for the new AC-MOT CAES are detailed in this thesis. This includes details of the atom trapping system, the photoionisation system, the electron extraction system and the various timing systems for creation and characterisation of the resultant cold electron bunches. Finally, the characterisation of the AC-MOT CAES itself is presented, and the measured beam metrics are used to compare the new AC-MOT CAES with other CAES designs which are under development.

Michael Jones, Matthew Harvey, William Alan Bertsche +4 more

A new cold atom electron source based on an AC-driven magneto-optical trap (AC-MOT) is described for electron diffraction studies. The advantages of the new source which uses an AC-MOT are detailed.

B. Ueberholz, V. Gomer, Svenja A. Knappe +2 more