63 research outputs found
Cavity-enhanced photoionization of an ultracold rubidium beam for application in focused ion beams
A two-step photoionization strategy of an ultracold rubidium beam for
application in a focused ion beam instrument is analyzed and implemented. In
this strategy the atomic beam is partly selected with an aperture after which
the transmitted atoms are ionized in the overlap of a tightly cylindrically
focused excitation laser beam and an ionization laser beam whose power is
enhanced in a build-up cavity. The advantage of this strategy, as compared to
without the use of a build-up cavity, is that higher ionization degrees can be
reached at higher currents. Optical Bloch equations including the
photoionization process are used to calculate what ionization degree and
ionization position distribution can be reached. Furthermore, the ionization
strategy is tested on an ultracold beam of Rb atoms. The beam current is
measured as a function of the excitation and ionization laser beam intensity
and the selection aperture size. Although details are different, the global
trends of the measurements agree well with the calculation. With a selection
aperture diameter of 52 m, a current of pA is
measured, which according to calculations is 63% of the current equivalent of
the transmitted atomic flux. Taking into account the ionization degree the ion
beam peak reduced brightness is estimated at A/(msreV).Comment: 13 pages, 9 figure
An intense, slow and cold beam of metastable Ne(3s) ^3P_2 atoms
We employ laser cooling to intensify and cool an atomic beam of metastable
Ne(3s) atoms. Using several collimators, a slower and a compressor we achieve a
^{20}Ne^* flux of 6 10^{10} atoms/s in an 0.7 mm diameter beam traveling at 100
m/s, and having longitudinal and transverse temperatures of 25mK and 300microK,
respectively. This constitutes the highest flux in a concentrated beam achieved
to date with metastable rare gas atoms. We characterize the action of the
various cooling stages in terms of their influence on the flux, diameter and
divergence of the atomic beam. The brightness and brilliance achieved are 2.1
10^{21} s^{-1} m^{-2} sr^{-1} and 5.0 10^{22} s^{-1} m^{-2} sr^{-1},
respectively, comparable to the highest values reported for alkali-metal beams.
Bright beams of the ^{21}Ne and ^{22}Ne isotopes have also been created.Comment: 18 pages, 9 figures, RevTe
Direct magneto-optical compression of an effusive atomic beam for high-resolution focused ion beam application
An atomic rubidium beam formed in a 70 mm long two-dimensional
magneto-optical trap (2D MOT), directly loaded from a collimated Knudsen
source, is analyzed using laser-induced fluorescence. The longitudinal velocity
distribution, the transverse temperature and the flux of the atomic beam are
reported. The equivalent transverse reduced brightness of an ion beam with
similar properties as the atomic beam is calculated because the beam is
developed to be photoionized and applied in a focused ion beam. In a single
two-dimensional magneto-optical trapping step an equivalent transverse reduced
brightness of A/(m sr eV) was
achieved with a beam flux equivalent to nA. The
temperature of the beam is further reduced with an optical molasses after the
2D MOT. This increased the equivalent brightness to A/(m sr eV). For currents below 10 pA, for which disorder-induced
heating can be suppressed, this number is also a good estimate of the ion beam
brightness that can be expected. Such an ion beam brightness would be a six
times improvement over the liquid metal ion source and could improve the
resolution in focused ion beam nanofabrication.Comment: 10 pages, 8 figures, 1 tabl
Measurement of the temperature of an ultracold ion source using time-dependent electric fields
We report on a measurement of the characteristic temperature of an ultracold
rubidium ion source, in which a cloud of laser-cooled atoms is converted to
ions by photo-ionization. Extracted ion pulses are focused on a detector with a
pulsed-field technique. The resulting experimental spot sizes are compared to
particle-tracking simulations, from which a source temperature
mK and the corresponding transversal reduced emittance m rad are determined. We find that this result is
likely limited by space charge forces even though the average number of ions
per bunch is 0.022.Comment: 8 pages, 11 figure
Approaching Bose-Einstein condensation of metastable neon:Over 10<sup>9</sup> trapped atoms
We present an experimental study of the loading of a magneto-optical trap (MOT) from a brightened and slowed beam of metastable neon atoms. The unprecedented high numbers of 9×10920Ne and 3×109 22Ne metastable atoms are trapped under unconventional trap conditions as compared to metastable helium traps, such as low intensity and small detuning. These cause the MOT to have an extraordinarily large volume on the order of 1cm3 and a typical peak density of 1010 atoms/cm3. A simple Doppler model is discussed which explains why the optimum is found under these conditions. The model includes the seventh beam necessary for the last slowing step before loading
Performance predictions for a laser intensified thermal beam for use in high resolution Focused Ion Beam instruments
Photo-ionization of a laser-cooled and compressed atomic beam from a
high-flux thermal source can be used to create a high-brightness ion beam for
use in Focus Ion Beam (FIB) instruments. Here we show using calculations and
Doppler cooling simulations that an atomic rubidium beam with a brightness of
at a current of 1 nA can be created using a
compact 5 cm long 2D magneto-optical compressor which is more than an order of
magnitude better than the current state of the art Liquid Metal Ion Source.Comment: 8 pages, 7 figures submitted to: Phys. Rev.
Simulated performance of an ultracold ion source
At present, the smallest spot size which can be achieved with state-of-the-art focused ion beam (FIB) 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 105 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
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