The possibility of departures from thermal equilibrium conditions in emission of ions from high temperature surfaces is investigated by pulsed ion extraction outside a surface ionization emitter. The ionization of Cs diffusing out from a carbon covered Ir foil emitter is studied, since static ionization studies have shown that large fluxes of highly excited Rydberg states are formed in this system. Short pulses down to ground potential are applied to a grid in front of the emitter. This gives an ion accelerating field strength of up to 1000V cm −1, which is enough to field-ionize Rydberg-type Cs atoms. The ion signal is analyzed with a partially energy compensated time-of-flight (TOF) mass spectrometer. Three Cs peaks are observed in the TOF spectrum. The first peak, which is related in time to the first field transition to the ion accelerating mode, is formed by field ionization outside the emitter and normally also by surface ionization on the emitter. The second and third peaks, which are related to the second field transition, are mainly due to field ionization. Other mass peaks, such as Cs 2+ and cluster peaks, are also observed, which shows that excited states are formed in the ion source.