We demonstrate an atom detector based on field ionization and subsequent ion counting. We make use of field enhancement near tips of carbon nanotubes to reach extreme electrostatic field values of up to $9\ifmmode\times\else\texttimes\fi{}{10}^{9}\text{ }\text{V}/\text{m}$, which ionize ground-state rubidium atoms. The detector is based on a carpet of multiwall carbon nanotubes grown on a substrate and used for field ionization, and a channel electron multiplier used for ion counting. We measure the field enhancement at the tips of carbon nanotubes by field emission of electrons. We demonstrate the operation of the field ionization detector by counting atoms from a thermal beam of a rubidium dispenser source. By measuring the ionization rate of rubidium as a function of the applied detector voltage we identify the field ionization distance, which is below a few tens of nanometers in front of nanotube tips. We deduce from the experimental data that field ionization of rubidium near nanotube tips takes place on a time scale faster than ${10}^{\ensuremath{-}10}\text{ }\text{s}$. This property is particularly interesting for the development of fast atom detectors suitable for measuring correlations in ultracold quantum gases. We also describe an application of the detector as partial pressure gauge.
We have excited helium atoms from their metastable 2
3S state to Rydberg states in the range
13<n<50 in a two-step process via the 3
3P state using light at $\ensuremath{\lambda}=389$ nm and 785--815 nm. Atoms in a thermal beam (100 K) cross partially overlapping laser beams of the appropriate frequencies in the counterintuitive order to exploit the high efficiency of stimulated rapid adiabatic passage. The interaction region is between two plates that can be used for Stark tuning in a few V/cm field or for field ionization. At fields much too low for field ionization, we observe signals attributed to ionization by blackbody radiation. Multiple tests confirm this attribution as the cause of ionization. For example, by heating the plates we observe the expected signal increases. Our experiments reinforce previous work where the interaction between Rydberg atoms and room temperature blackbody radiation is important for experiments.