16 research outputs found
Cold trapped atoms detected with evanescent waves
We demonstrate the in situ detection of cold 87 Rb atoms near a dielectric
surface using the absorption of a weak, resonant evanescent wave. We have used
this technique in time of flight experiments determining the density of atoms
falling on the surface. A quantitative understanding of the measured curve was
obtained using a detailed calculation of the evanescent intensity distribution.
We have also used it to detect atoms trapped near the surface in a
standing-wave optical dipole potential. This trap was loaded by inelastic
bouncing on a strong, repulsive evanescent potential. We estimate that we trap
1.5 x 10 4 atoms at a density 100 times higher than the falling atoms.Comment: 5 pages, 3 figure
Theoretical study of a cold atom beam splitter
A theoretical model is presented for the study of the dynamics of a cold
atomic cloud falling in the gravity field in the presence of two crossing
dipole guides. The cloud is split between the two branches of this laser guide,
and we compare experimental measurements of the splitting efficiency with
semiclassical simulations. We then explore the possibilities of optimization of
this beam splitter. Our numerical study also gives access to detailed
information, such as the atom temperature after the splitting
Guiding of cold atoms by a red-detuned laser beam of moderate power
We report measurements on the guiding of cold Rb atoms from a
magneto-optical trap by a continuous light beam over a vertical distance of 6.5
mm. For moderate laser power (85 mW) we are able to capture around 40% of
the cold atoms. Although the guide is red-detuned, the optical scattering rate
at this detuning (70 GHz) is acceptably low. For lower detuning (30
GHz) a larger fraction was guided but radiation pressure starts to push the
atoms upward, effectively lowering the acceleration due to gravity. The
measured guided fraction agrees well with an analytical model.Comment: final version, 6 pages, incl. 6 figure
A rainbow of cold atoms caused by a stochastic process
We report direct observation of a rainbow caustic in the velocity distribution of ^{87}Rb atoms, bouncing inelastically on an evanescent-wave atom mirror. In contrast to known examples, this caustic is caused by a stochastic process, namely a spontaneous Raman transition during the bounce. The results are in good agreement with a classical calculation. We observed that although energy is extracted from the atoms, the phase-space density is in most cases not increased
Creating a low-dimensional quantum gas using dark states in an inelastic evanescent-wave mirror
We discuss an experimental scheme to create a low-dimensional gas of
ultracold atoms, based on inelastic bouncing on an evanescent-wave mirror.
Close to the turning point of the mirror, the atoms are transferred into an
optical dipole trap. This scheme can compress the phase-space density and can
ultimately yield an optically-driven atom laser. An important issue is the
suppression of photon scattering due to ``cross-talk'' between the mirror
potential and the trapping potential. We propose that for alkali atoms the
photon scattering rate can be suppressed by several orders of magnitude if the
atoms are decoupled from the evanescent-wave light. We discuss how such dark
states can be achieved by making use of circularly-polarized evanescent waves.Comment: 8 pages, 4 figure
Observation of radiation pressure exerted by evanescent waves
We report a direct observation of radiation pressure, exerted on cold
rubidium atoms while bouncing on an evanescent-wave atom mirror. We analyze the
radiation pressure by imaging the motion of the atoms after the bounce. The
number of absorbed photons is measured for laser detunings ranging from {190
MHz} to {1.4 GHz} and for angles from {0.9 mrad} to {24 mrad} above the
critical angle of total internal reflection. Depending on these settings, we
find velocity changes parallel with the mirror surface, ranging from 1 to {18
cm/s}. This corresponds to 2 to 31 photon recoils per atom. These results are
independent of the evanescent-wave optical power.Comment: 6 pages, 4 figure