We report a measurement of the ion recoil energy in photoionization of laser-cooled atoms.
87Rb, cooled in a magneto-optical trap, is two-photon ionized by a pulsed laser. The recoil energy is determined by time-of-flight in a weak electric field. A resolution in the range of 1 \ensuremath{\mu}eV is demonstrated. Refinement of the technique promises resolution in the range of several neV to be feasible.
We have used a cold ( T<<1 mK), laser-cooled target of Na atoms confined in a magneto-optical trap to study electron capture processes during highly charged ion-sodium atom collisions at keV energies. Momentum distributions of target ions were determined by employing time-of-flight and position sensitive detection of the Na ions, produced during the collisions and extracted by a weak electric field. In this way impact parameter sensitive information about multielectron capture processes is obtained.
A reaction microscope (ReMi) has been combined with a magneto-optical trap (MOT) for the kinematically complete investigation of atomic break-up processes. With the novel MOTReMi apparatus, the momentum vectors of the fragments of laser-cooled and state-prepared lithium atoms are measured in coincidence and over the full solid angle. The first successful implementation of a MOTReMi could be realized due to an optimized design of the present setup, a nonstandard operation of the MOT, and by employing a switching cycle with alternating measuring and trapping periods. The very low target temperature in the MOT (∼2 mK) allows for an excellent momentum resolution. Optical preparation of the target atoms in the excited Li 2(2)P3/2 state was demonstrated providing an atomic polarization of close to 100%. While first experimental results were reported earlier, in this work, we focus on the technical description of the setup and its performance in commissioning experiments involving target ionization in 266 nm laser pulses and in collisions with projectile ions.
Photoionization of rubidium atoms cooled in a magneto-optical trap, characterized by the coexistence of the ground
5S1/2 and excited
5P3/2 states, is investigated experimentally and theoretically with the 400-nm femtosecond laser pulses at intensities of $I=(3\ifmmode\times\else\texttimes\fi{}{10}^{9})\text{--}(4.5\ifmmode\times\else\texttimes\fi{}{10}^{12})$
W/cm2. The recoil-ion momentum distribution (RIMD) of
Rb+ exhibits rich ringlike structures and their energies correspond to one-photon ionization of the
5P3/2 state and two-photon and three-photon ionizations of the
5S1/2 state, respectively. With increasing
I, the dips near zero momentum (NZM) in the experimental RIMDs become shallow dramatically and their peaked
Rb+ momenta ionized from the
5P3/2 state move obviously toward zero while the peaks from the
5S1/2 state do not shift. In addition, the ion-yield ratio of the
5S1/2 state to the
5P3/2 state varies from
I to
I1.5 as
I increases. These features indicate a transition from perturbative ionization to strongly perturbative ionization for the
5P3/2 state. Numerical simulations by solving the time-dependent Schr\"odinger equation (TDSE) can qualitatively explain the measurements of the RIMD, photoion angular distributions, and ion-yield ratio. However, some discrepancies still exist, especially for the NZM dip, which could stem from the electron-electron correlation that is neglected in the present TDSE simulations since we have adopted the single-active-electron approximation.
We study photoionization of cold rubidium atoms in a strong infrared laser field using a magneto-optical trap (MOT) recoil ion momentum spectrometer. Three types of cold rubidium target are provided, operating in two-dimension (2D) MOT, 2D molasses, and 3D MOT with densities in the orders of
107 atoms/cm
3,
108 atoms/cm
3, and
109 atoms/cm
3, respectively. The density profile and the temperature of 3D MOT are characterized using the absorption imaging and photoionization. The momentum distributions of Rb
+ created by absorption of two- or three-photon illuminate a dipole-like double-peak structure, in good agreement with the results in the strong field approximation. The yielding momentum resolution of
0.12±0.03 a.u. is achieved in comparison with theoretical calculations, exhibiting the great prospects for the study of electron correlations in alkali metal atoms through interaction with strong laser pulses.
Synopsis We report on performing high resolution recoil ion momentum spectroscopy in a reaction microscope (ReMi) on a target of dipole-force trapped cold 6Li atoms in a non-interacting |1〉-|2〉 spin mixture and coincident detection of recoil ions and photoelectrons. Photo-ionization occurs from the electronic ground state of the 6Li atoms and IR photons significantly contribute to the ion yield via 3-photon resonances. High resolution time-of-flight spectra are obtained by modulating the trap depth synced with the arrival of the fs laser pulses.