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Optical collisions in crossed beams and Bose-Einstein condensation in a microtrap

C. Figl

Published Jan 1, 2004• 1 citation

Abstract

Optical collisions are studied in a crossed beams experiment. Differential cross sections of K-Ar collisions are measured and are used to derive the repulsive parts of the XΣ and BΣ potential curves. The achieved accuracy has not been realized with scattering experiments before. A collision energy resolved analysis of the final state probes the relative population of the fine-structure states K(4p1/2) and K(4p3/2) which depends on details of the outer part of the potentials. Calculations from the determined potentials are in concordance with the experimental results. The relative population of the Na fine-structure states after Na-N2 and Na-O2 collisions is determined similarly. The results for N2 are in very good agreement with the theory. Differential cross sections of Ca-Ar optical collisions are measured for an asymptotically forbidden transition. The spectral dependence of the signal intensity shows a characteristic maximum. The experimental data are in good agreement with ab initio calculations. Wires on a microchip create a magnetic trap that is used to obtain a Rb-87 Bose-Einstein condensate. The roughness of the magnetic potential is characterized by the measured density of a cold atom cloud. The measured roughness is compared to the roughness that is calculated from the geometry of the microwire.

DOI: 10.15488/6342

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Optical collisions are studied in a crossed beams experiment. Differential cross sections of K-Ar collisions are measured and are used to derive the repulsive parts of the XΣ and BΣ potential curves. The achieved accuracy has not been realized with scattering experiments before. A collision energy resolved analysis of the final state probes the relative population of the fine-structure states K(4p1/2) and K(4p3/2) which depends on details of the outer part of the potentials. Calculations from the determined potentials are in concordance with the experimental results. The relative population of the Na fine-structure states after Na-N2 and Na-O2 collisions is determined similarly. The results for N2 are in very good agreement with the theory. Differential cross sections of Ca-Ar optical collisions are measured for an asymptotically forbidden transition. The spectral dependence of the signal intensity shows a characteristic maximum. The experimental data are in good agreement with ab initio calculations. Wires on a microchip create a magnetic trap that is used to obtain a Rb-87 Bose-Einstein condensate. The roughness of the magnetic potential is characterized by the measured density of a cold atom cloud. The measured roughness is compared to the roughness that is calculated from the geometry of the microwire.

Differential cross sections for the transition K(4

{P}_{3/2}

\ensuremath{\rightarrow}4

{P}_{1/2}

) induced by He and Ar have been studied both experimentally and theoretically. Calculations were performed using a full quantal close-coupling formalism. The angular distribution of the scattered atoms is measured by Doppler shift (ADDS method). The comparison with the theoretical calculations is performed on the basis of thorough kinematic analysis. In addition, the polarization effects corresponding to the experimental conditions are taken into account carefully. This allows one to test the accuracy of various interaction potentials available for the K-He and -Ar systems. The most interesting result concerns the K-He l-dependent pseudopotentials, which are found accurate to a sufficiently high level to allow good predictions of the observed differential cross-section patterns. In particular the positions and amplitudes of the cross-section oscillations at large center-of-mass scattering angles are well reproduced. The results for Ar show that the K-Ar potentials must be improved. Finally, taking the K(4P)-He fine-structure transition as an example, it has been shown how polarization effects may be used in ADDS measurements to obtain information on the dynamics of the collision process.

The optical collision Na(3s)+Kr+hν→Na(3p)+Kr has been investigated in an experiment with crossed atomic beams and with a differential detection of the excited collision products. Three groups of experimental results have been obtained, which all demonstrate unprecedented possibilities for the observation of atomic collisions. 1. The oscillatory structure of the differential cross sections allows a sensitive test of the molecular potentials. 2. Polarization experiments give direct information about the geometric characteristics of the collision complex. 3. State analysis of the collision products provides a tool for the observation of elementary nonadiabatic processes. A number of possible future experiments, which make use of the new ideas, is discussed, in addition.

Optical collisions in a crossed beam experiment are examined for the atomic collision pairs LiHe, LiNe, NaNe.Differential cross sections are measured in order to probe the quallity of quantum chemical calculated and spectroscopical determined molecular potentials.The linear polarization of the excitation laser is used to manipulate the contrast of the differential cross sections for NaNe.Using elliptical polarized light total control over the angular position and the contrast of the interference pattern is demonstrated.Differential cross sections for the collision pairs LiH and LiD show a pronounced oscillatory structure, which for the first time is observed for atom-molecule optical collisions.

The nonadiabatic close-coupled theory of atomic collisions in a radiation field is generalized to include electron spin and is used to consider the weak-field Na--rare-gas (RG) optical collision Na

{(}^{2}

{S}_{1/2}

)+RG+nh\ensuremath{\nu} \ensuremath{\mu}Na

{(}^{2}

{\mathrm{P}}_{\mathrm{j}}

)+RG+(n-1)h\ensuremath{\nu}. The effects of detuning and incident energy on the branching into the atomic Na 3

{p}^{2}

{P}_{3/2}

and 3p

^{2}P_{1/2}

states are examined. The cross sections \ensuremath{\sigma}(j) are found to have a strong asymmetry between red and blue detuning as well as a complex threshold and resonance structure dependence on energy. A partial cross-section analysis of \ensuremath{\sigma}(j) shows a significant difference between contributions from states of e and f molecular parity. The theoretically calculated detuning dependence of the branching ratio into each fine-structure state is in good agreement with available experimental data for Na-Ar, Na-Ne, and Na-He, as well as the total absorption coefficient for the production of Na 3p atoms. The fine-structure branching ratio for thermal energy collisions shows considerable variation with a rare-gas collision partner, due to the different interaction potentials. For sufficiently high collision energy, the branching approaches a recoil limit which is independent of collision partner.