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arXiv:1712.01200 · Physical Review A

All-optical atom trap as a target for MOTRIMS-like collision experiments

Sachin Sharma, B. P. Acharya, A. H. N. C. De Silva, N. W. Parris, B. J. Ramsey, K. L. Romans, Alexander Dorn, Vitor L. B. de Jesus, D. Fischer

Published Apr 25, 2018• 18 citations

Abstract

Momentum-resolved scattering experiments with laser-cooled atomic targets have been performed since almost two decades with magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) setups. Compared to experiments with gas-jet targets, MOTRIMS features significantly lower target temperatures allowing for an excellent recoil ion momentum resolution. However, the coincident and momentum-resolved detection of electrons was long rendered impossible due to incompatible magnetic field requirements. Here we report on an experimental approach which is based on an all-optical $^{6}\mathrm{Li}$ atom trap that---in contrast to magneto-optical traps---does not require magnetic field gradients in the trapping region. Atom temperatures of about 2 mK and number densities up to ${10}^{9}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ make this trap ideally suited for momentum-resolved electron-ion coincidence experiments. The overall configuration of the trap is very similar to conventional magneto-optical traps. It mainly requires small modifications of laser beam geometries and polarization which makes it easily implementable in other existing MOTRIMS experiments.

DOI: 10.1103/physreva.97.043427

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Momentum-resolved scattering experiments with laser-cooled atomic targets have been performed since almost two decades with magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) setups. Compared to experiments with gas-jet targets, MOTRIMS features significantly lower target temperatures allowing for an excellent recoil ion momentum resolution. However, the coincident and momentum-resolved detection of electrons was long rendered impossible due to incompatible magnetic field requirements. Here we report on an experimental approach which is based on an all-optical

^{6}\mathrm{Li}

atom trap that---in contrast to magneto-optical traps---does not require magnetic field gradients in the trapping region. Atom temperatures of about 2 mK and number densities up to

{10}^{9}

{\mathrm{cm}}^{\ensuremath{-}3}

make this trap ideally suited for momentum-resolved electron-ion coincidence experiments. The overall configuration of the trap is very similar to conventional magneto-optical traps. It mainly requires small modifications of laser beam geometries and polarization which makes it easily implementable in other existing MOTRIMS experiments.

A new MOTRIMS (magneto-optical trap-target recoil ion momentum spectroscopy) apparatus has been built at the LPC-CAEN, and recently tested with a beam of 2 keV Na + projectiles colliding on a trapped Rb target. In this work, we demonstrate the capability of the setup to provide, with a very high signal over background ratio, fully differential cross sections in scattering angle, initial state, and final state of the system. The fine control of the trapping lasers, the extraction of the recoil ions transverse to the ion beam axis, and the fast switching for the MOT magnetic field, are three characteristics promising for new studies including collisions with oriented targets or requiring electron detection.

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The trapping lasers of a magneto-optical trap have been used to bring Rb atoms into well defined oriented states. Coupled to recoil-ion-momentum spectroscopy, this provided a unique MOTRIMS setup which was able to probe scattering dynamics, including the coherence features, with unprecedented resolution. The technique was applied to the low-energy charge exchange reactions Na+ + Rb(5p±1)→Na(3p,4s)+Rb+. The measurements revealed detailed features of the collisional interaction which were employed to improve the theoretical description. As such, it was possible to ascertain the validity of the intuitive models used to predict the most likely capture transitions.