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Register a new userSelf-driven nonlinear dynamics in magneto-optical traps
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We present a theoretical model describing recently observed collective effects in large magneto-optically trapped atomic ensembles. Based on a kinetic description we develop an efficient test particle method, which in addition to the single atom light pressure accounts for other relevant effects such as laser attenuation and forces due to multiply scattered light with position dependent absorption cross sections. Our calculations confirm the existence of a dynamical instability and provide deeper insights into the observed system dynamics.
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We study several new magneto-optical trapping configurations in $^{87}$Rb. These unconventional MOTs all use type-II transitions, where the angular momentum of the ground state is greater than or equal to that of the excited state, and they may use either red-detuned or blue-detuned light. We describe the conditions under which each new MOT forms. The various MOTs exhibit an enormous range of lifetimes, temperatures and density distributions. At the detunings where they are maximized, the lifetimes of the various MOTs vary from 0.1 to 15 s. One MOT forms large ring-like structures with no density at the centre. The temperature in the red-detuned MOTs can be three orders of magnitude higher than in the blue-detuned MOTs. We present measurements of the capture velocity of a blue-detuned MOT, and we study how the loss rate due to ultracold collisions depends on laser intensity and detuning.
We have used diffraction gratings to simplify the fabrication, and dramatically increase the atomic collection efficiency, of magneto-optical traps using micro-fabricated optics. The atom number enhancement was mainly due to the increased beam capture volume, afforded by the large area (4cm^2) shallow etch (200nm) binary grating chips. Here we provide a detailed theoretical and experimental investigation of the on-chip magneto-optical trap temperature and density in four different chip geometries using 87Rb, whilst studying effects due to MOT radiation pressure imbalance. With optimal initial MOTs on two of the chips we obtain both large atom number (2x10^7) _and_ sub-Doppler temperatures (50uK) after optical molasses.
Direct loading of lanthanide atoms into magneto-optical traps (MOTs) from a very slow cryogenic buffer gas beam source is achieved, without the need for laser slowing. The beam source has an average forward velocity of 60-70,m/s and a velocity half-width of ~35 m/s, which allows for direct MOT loading of Yb, Tm, Er and Ho. Residual helium background gas originating from the beam results in a maximum trap lifetime of about 80 ms (with Yb). The addition of a single-frequency slowing laser applied to the Yb in the buffer gas beam increases the number of trapped Yb atoms to 1.3(0.7) x 10^8 with a loading rate of 2.0(1.0) x 10^10 atoms/s. Decay to metastable states is observed for all trapped species and decay rates are measured. Extension of this approach to the loading of molecules into a MOT is discussed.
We predict theoretically and demonstrate experimentally an ellipticity-dependent nonlinear magneto-optic rotation of elliptically-polarized light propagating in a coherent atomic medium. We show that this effect results from a hexadecapole and higher order momenta of atomic coherence, and is associated with an enhancement of Kerr and higher orders nonlinearities accompanied by suppression of the other linear and nonlinear susceptibility terms of the medium. These nonlinearities might be useful for quantum signal processing. In particular, we report an observation of an enhancement the polarization rotation of elliptically polarized light resonant with the 5S_{1/2} F=2 -> 5P_{1/2} F=1 transition of Rb87.
We have studied magneto-optical traps (MOTs) for efficient on-line trapping of radioactive atoms. After discussing a model of the trapping process in a vapor cell and its efficiency, we present the results of detailed experimental studies on Rb MOTs. Three spherical cells of different sizes were used. These cells can be easily replaced, while keeping the rest of the apparatus unchanged: atomic sources, vacuum conditions, magnetic field gradients, sizes and power of the laser beams, detection system. By direct comparison, we find that the trapping efficiency only weakly depends on the MOT cell size. It is also found that the trapping efficiency of the MOT with the smallest cell, whose diameter is equal to the diameter of the trapping beams, is about 40% smaller than the efficiency of larger cells. Furthermore, we also demonstrate the importance of two factors: a long coated tube at the entrance of the MOT cell, used instead of a diaphragm; and the passivation with an alkali vapor of the coating on the cell walls, in order to minimize the losses of trappable atoms. These results guided us in the construction of an efficient large-diameter cell, which has been successfully employed for on-line trapping of Fr isotopes at INFNs national laboratories in Legnaro, Italy.
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