At present, the smallest spot size which can be achieved with state-of-the-art focused ion beam ͑FIB͒ technology is mainly limited by the chromatic aberrations associated with the 4.5 eV energy spread of the liquid-metal ion source. Here we numerically investigate the performance of an ultracold ion source which has the potential for generating ion beams which combine high brightness with small energy spread. The source is based on creating very cold ion beams by near-threshold photoionization of a laser-cooled and trapped atomic gas. We present ab initio numerical calculations of the generation of ultracold beams in a realistic acceleration field and including all Coulomb interactions, i.e., both space charge effects and statistical Coulomb effects. These simulations demonstrate that with existing technology reduced brightness values exceeding 10 5 A m −2 sr −1 V −1 are feasible at an energy spread as low as 0.1 eV. The estimated spot size of the ultracold ion source in a FIB instrument ranges from 10 nm at a current of 100 pA to 0.8 nm at 1 pA.

No abstract

We describe here a specially designed accelerator structure and a pulsed power supply that are essential parts of a high brightness cold atoms-based electron source. The accelerator structure allows a magnetooptical atom trap to be operated inside of it, and also transmits subnanosecond electric field pulses. The power supply produces high voltage pulses up to 30 kV, with a rise time of up to 30 ns. The resulting electric field inside the structure is characterized with an electro-optic measurement and with an ion timeof-flight experiment. Simulations predict that 100 fC electron bunches, generated from trapped atoms inside the structure, reach an emittance of 0.04 mm mrad and a bunch length of 80 ps.

Ultracold electron sources, which are based on near-threshold photo- and field-ionization of a cloud of laser-cooled atoms, offer the unique combination of low emittance and extended size that is essential for achieving single-shot, ultrafast electron diffraction of macromolecules. Here we present measurements of the effective temperature of such a pulsed electron source employing rubidium atoms that are magneto-optically trapped at the center of an accelerator structure. Transverse source temperatures ranging from 200 K down to 10 K are demonstrated, controllable with the wavelength of the ionization laser. Together with the 50 μm source size, the achievable temperature enables a transverse coherence length of ≈20 nm for a 100 μm sample size.

A novel way of creating low-temperature electron and ion beams is demonstrated. The beams are generated by converting a laser-cooled atom cloud to a highly excited Rydberg gas, which subsequently develops into an ultracold plasma. Charged particles are extracted from the Rydberg gas and the plasma by a pulsed electric field. The properties of the resulting electron and ion pulses are experimentally studied. Pulses of a few hundred ns duration containing a few pC of charge were observed. Upper limits for the temperature of such beams (60K for ions and 500K for electrons) are obtained, and the beams are shown to have low emittance. Further development of the method may lead to the generation of high-brightness charged-particle beams from ultracold plasmas.