A supersonic beam of hydrogen molecules is crossed by two laser beams which excite the H2 into Rydberg states with principal quantum number n ~ 20 at a distance of 2-3 mm above a metal surface.
The beam is directed at a grazing incidence angle (5-7°) with respect to the surface.
After 5 – 10 ms, the Rydberg molecules interact with the surface, with ionization occurring at around 80nm from the surface ( n = 20).
At the moment we are mainly studying the ionization of the Rydberg molecules at the surface, but future experiments will explore competing processes.
To do this we allow the interaction to happen in the presence of an electric field that will tend to pull either the ions or the electrons formed in this process away from the surface towards a charged particle detector
In the experimental result above we have measured the production of ions through surface ionization as a function of extraction field. For ionization at a given distance from the surface a minimum field is required to pull the ion to the detector. Thus the above graph allows us to determine the distances of ionization for different principal quantum numbers. It indicates the expected increase of ionization distance with principal quantum number.