Radiative collisional heating at the Doppler limit for laser-cooled magnesium atoms

We report Monte Carlo wave function simulation results on cold collisions between magnesium atoms in a strong red-detuned laser field. This is the normal situation e.g. in magneto-optical traps (MOT). The Doppler limit heating rate due to radiative collisions is calculated for Mg-24 atoms in a magneto-optical trap based on the singlet S_0 - singlet P_1 atomic laser cooling transition. We find that radiative heating does not seem to affect the Doppler limit in this case. We also describe a channelling mechanism due to the missing Q branch in the excitation scheme, which could lead to a suppression of inelastic collisions, and find that this mechanism is not present in our simulation results due to the multistate character of the excitation process.Comment: 4 pages, RevTeX 4; v2 contains minor revisions based on referee comments (5 pages

Photoassociation spectroscopy of cold alkaline earth atoms near the intercombination line

The properties of photoassociation (PA) spectra near the intercombination line (the weak transition between $^{1}S_{0}$ and $^{3}P_{1}$ states) of group II atoms are theoretically investigated. As an example we have carried out a calculation for Calcium atoms colliding at ultra low temperatures of 1 mK, 1 $\mu$K, and 1 nK. Unlike in most current photoassociation spectroscopy the Doppler effect can significantly affect the shape of the investigated lines. Spectra are obtained using Ca--Ca and Ca--Ca$^*$ short-range {\it ab initio} potentials and long-range van der Waals and resonance dipole potentials. The similar van der Waals coefficients of ground $^{1}S_{0} + ^{1}S_{0}$ and excited $^{1}S_{0} + ^{3}P_{1}$ states cause the PA to differ greatly from those of strong, allowed transitions with resonant dipole interactions. The density of spectral lines is lower, the Condon points are at relatively short range, and the reflection approximation for the Franck-Condon factors is not applicable, and the spontaneous decay to bound ground-state molecules is efficient. Finally, the possibility of efficient production of cold molecules is discussed

Study of coupled states for the (4s^{2})^{1}S + (4s4p)^{3}P asymptote of Ca_{2}

The coupled states A^{1}\Sigma_{u}^{+} (^{1}D +}1}S), c^{3}\Pi_{u} (^{3}P + ^{1}S) and a^{3}\Sigma_{u}^{+} (^{3}P +}1}S) of the calcium dimer are investigated in a laser induced fluorescence experiment combined with high-resolution Fourier-transform spectroscopy. A global deperturbation analysis of the observed levels, considering a model, which is complete within the subspace of relevant neighboring states, is performed using the Fourier Grid Hamiltonian method. We determine the potential energy curve of the A^{1}\Sigma_{u}^{+} and c^{3}\Pi_{u} states and the strengths of the couplings between them. The c^{3}\Pi_{u} and \as states are of particular importance for the description of collisional processes between calcium atoms in the ground state ^{1}S_{0} and excited state ^{3}P_{1} applied in studies for establishing an optical frequency standard with Ca.Comment: 15 pages, 12 figure

Scattering length of the ground state Mg+Mg collision

We have constructed the X 1SIGMAg+ potential for the collision between two ground state Mg atoms and analyzed the effect of uncertainties in the shape of the potential on scattering properties at ultra-cold temperatures. This potential reproduces the experimental term values to 0.2 inverse cm and has a scattering length of +1.4(5) nm where the error is prodominantly due to the uncertainty in the dissociation energy and the C6 dispersion coefficient. A positive sign of the scattering length suggests that a Bose-Einstein condensate of ground state Mg atoms is stable.Comment: 15 pages, 3 figures, Submitted Phys. Rev.

Theoretical study of collisional redistribution of light near the resonance of the Ba, Sr and Mg atoms perturbed by He and Ne

Absorption coefficient and polarization of collisionally redistributed fluorescence light in a range of detunings around the atomic resonance have been calculated for Ba, Sr and Mg perturbed by He and Ne. Results are obtained from fully-quantum mechanical coupled-channels calculations including the relevant ground and two excited $^1\Sigma$ and $^1\Pi$ molecular states for each diatomic. Close-coupling calculations are carried out based on the theoretical potential curves obtained by means of a pseudopotential + valence configuration-interaction (CI) technique. For accurate comparison with experiment the calculated absorption coefficients and polarizations have been thermally averaged over the collision energy. The theoretical absorption profiles and linear polarization ratios agree, in general, quite well with the available experimental data