Manipulation and control of molecular beams

State-selective manipulation of atoms and molecules with electric and magnetic fields has been crucial for the success of the field of molecular beams. Originally, this manipulation only involved the transverse motion. In the first part of my Lecture, I will present an historical overview of the development of the Stark-decelerator, that enables to also manipulate and control the longitudinal motion of neutral, polar molecules in a beam. Together with other elements like a buncher, a storage ring and a synchrotron - all well-known for charged particles - a whole new toolbox for molecular beam research has emerged [1].

In the second part of my Lecture, I will report on our molecular beam experiments on chiral molecules and on experiments to laser cool and trap diatomic molecules. In the study of chiral molecules, photo- electron circular dichroism (PECD) [2] - a forward-backward asymmetry in the photoemission from a non-racemic sample induced by circularly polarized light - and microwave three wave mixing (M3WM) [3] have emerged as powerful new techniques during the last decades. We have demonstrated that PECD can be observed for chiral molecules in solution as well as for anions in the gas phase. We have performed M3WM experiments on a jet-cooled beam of 1-indanol, in a scheme that has enabled the first quantitative comparison of experiment and theory for the transfer efficiency in what is the simplest triangle for enantiomer-specific state transfer (ESST) for any chiral molecule, that is, the one involving the absolute ground state level [4]. In our search for "the most ideal molecule" for laser cooling and trapping, that is, yielding the highest densities of ultracold molecular samples, we have identified and focused in on aluminum monofluoride. The AlF molecule has a binding energy of almost 7 eV and a bright beam of AlF can be produced, either pulsed or cw. The photon scattering rate on the A1 P - X1 S+ band around 227 nm is very high, the Franck-Condon matrix is highly diagonal, all Q-lines of a 1 P ¬ 1 S+ transition are rotationally closed and the hyperfine splitting in the 1 S+ state is within the natural linewidth of the optical transition. The distance needed for laser slowing a beam of AlF molecules to rest will therefore be only several centimeters and the capture velocity of a MOT will be exceptionally large. We have used pulsed beams of jet-cooled AlF and beams from a buffergas source in combination with radio-frequency, microwave and optical fields to experimentally determine the properties of the lowest rotational levels in the X1 S+, A1 P and a3 P states of AlF [5, 6] and we have demonstrated efficient optical cycling on the A1 P - X1 S+band [7].

Speaker: Gerard Meijer, Fritz Haber Institute