Novel Experimental Approaches to Studies of Electron Metastable Atom Collisions

The radio-frequency paramagnetic-resonance method was used to observe the exchange collisions between the singly ionized Xe ground state $^{2}P_{\frac{3}{2}}$ and the neutral metastable state $^{3}P_{2}$ . The ionic ground-state and metastable-state atoms are both formed and aligned by unidirectional low-energy high-flux electron-beam impact. The magnetic resonances of even and odd ionic ground-state atoms were observed by monitoring changes in the transparency of the resonance radiation absorbed by the metastable-state atoms. Phenomenological theories are presented which explain the sign of the magnetic-resonance signal of the ionic ground state relative to that of the neutral metastable state, together with independent experimental evidence to support the theories. Conclusive experimental evidence is presented supporting our original assumptions that the ionic ground-state ${\mathrm{Xe}}^{+}(^{2}P_{\frac{3}{2}})$ is aligned by low-energy electron-impact ionization and that such alignment is detectable through the results of exchange collisions with the metastable state.The radio-frequency paramagnetic-resonance method was used to observe the exchange collisions between the singly ionized Xe ground state $^{2}P_{\frac{3}{2}}$ and the neutral metastable state $^{3}P_{2}$. The ionic ground-state and metastable-state atoms are both formed and aligned by unidirectional low-energy high-flux electron-beam impact. The magnetic resonances of even and odd ionic ground-state atoms were observed by monitoring changes in the transparency of the resonance radiation absorbed by the metastable-state atoms. Phenomenological theories are presented which explain the sign of the magnetic-resonance signal of the ionic ground state relative to that of the neutral metastable state, together with independent experimental evidence to support the theories. Conclusive experimental evidence is presented supporting our original assumptions that the ionic ground-state ${\mathrm{Xe}}^{+}(^{2}P_{\frac{3}{2}})$ is aligned by low-energy electron-impact ionization and that such alignment is detectable through the results of exchange collisions with the metastable state.

Physical ReviewJun 5, 19685 citations

Bose-Einstein Condensation of Metastable Helium

Claude N. Cohen-Tannoudji

Two groups, in Orsay and in Paris, have recently obtained experimental evidence for Bose-Einstein condensation on He4 atoms in the metastable state 23S1. The condensates which have been obtained are the first ones where atoms are condensed, not in their electronic ground state, but in an excited state, in this case a metastable state about 20 eV above the ground state. In principle, Penning collisions should very rapidly destroy the cloud of cold metastable atoms and it seems hopeless to observe Bose-Einstein condensation in such a system. But, as suggested by Shlyapnikov et al, the conservation of the total spin during the collision reduces the Penning collision cross-sections by several orders of magnitude and this explains why large enough densities of metastable atoms can be obtained to observe the condensation. We briefly describe the first experimental results which have been obtained in Paris. Atoms are optically detected by optical imaging at 1083 nm (wavelength of the transition connecting the metastable state 23S1 to the triplet state 23P2). The evolution of the anisotropy of the images during a ballistic expansion gives clear evidence for the condensation. Orders of magnitude are also obtained for the scattering length describing the collision between 2 metastable atoms. The large value of this scattering length (of the order of 10 nm) allows one to reach the so called hydrodynamic regime where the mean free path between 2 collisions in the thermal cloud becomes smaller than the size of the cloud. Preliminary results showing the transition between the collisionless regime and the hydrodynamic regime are presented and compared to theoretical predictions.Two groups, in Orsay and in Paris, have recently obtained experimental evidence for Bose-Einstein condensation on He4 atoms in the metastable state 23S1. The condensates which have been obtained are the first ones where atoms are condensed, not in their electronic ground state, but in an excited state, in this case a metastable state about 20 eV above the ground state. In principle, Penning collisions should very rapidly destroy the cloud of cold metastable atoms and it seems hopeless to observe Bose-Einstein condensation in such a system. But, as suggested by Shlyapnikov et al, the conservation of the total spin during the collision reduces the Penning collision cross-sections by several orders of magnitude and this explains why large enough densities of metastable atoms can be obtained to observe the condensation. We briefly describe the first experimental results which have been obtained in Paris. Atoms are optically detected by optical imaging at 1083 nm (wavelength of the transition connecting the metastable state 23S1 to the triplet state 23P2). The evolution of the anisotropy of the images during a ballistic expansion gives clear evidence for the condensation. Orders of magnitude are also obtained for the scattering length describing the collision between 2 metastable atoms. The large value of this scattering length (of the order of 10 nm) allows one to reach the so called hydrodynamic regime where the mean free path between 2 collisions in the thermal cloud becomes smaller than the size of the cloud. Preliminary results showing the transition between the collisionless regime and the hydrodynamic regime are presented and compared to theoretical predictions.

Condensation and Coherence in Condensed MatterMar 1, 20030 citations

The radio-frequency paramagnetic-resonance method was used to observe the exchange collisions between the singly ionized Xe ground state

^{2}P_{\frac{3}{2}}

and the neutral metastable state

^{3}P_{2}

. The ionic ground-state and metastable-state atoms are both formed and aligned by unidirectional low-energy high-flux electron-beam impact. The magnetic resonances of even and odd ionic ground-state atoms were observed by monitoring changes in the transparency of the resonance radiation absorbed by the metastable-state atoms. Phenomenological theories are presented which explain the sign of the magnetic-resonance signal of the ionic ground state relative to that of the neutral metastable state, together with independent experimental evidence to support the theories. Conclusive experimental evidence is presented supporting our original assumptions that the ionic ground-state

{\mathrm{Xe}}^{+}(^{2}P_{\frac{3}{2}})

is aligned by low-energy electron-impact ionization and that such alignment is detectable through the results of exchange collisions with the metastable state.