Rb*He_n exciplexes in solid 4_He

We report the observation of emission spectra from Rb*He_n exciplexes in solid 4He. Two different excitation channels were experimentally identified, viz., exciplex formation via laser excitation to the atomic 5P3/2 and to the 5P1/2 levels. While the former channel was observed before in liquid helium, on helium nanodroplets and in helium gas by different groups, the latter creation mechanism occurs only in solid helium or in gaseous helium above 10 Kelvin. The experimental results are compared to theoretical predictions based on the extension of a model, used earlier by us for the description of Cs*He_n exciplexes. We also report the first observation of fluorescence from atomic rubidium in solid helium, and discuss striking differences between the spectroscopic feature of Rb-He and Cs-He systems.Comment: 8 pages, 8 figure

Towards redistribution laser cooling of molecular gases: Production of candidate molecules SrH by laser ablation

Laser cooling by collisional redistribution of radiation has been successfully applied in the past for cooling dense atomic gases. Here we report on progress of work aiming at the demonstration of redistribution laser cooling in a molecular gas. The candidate molecule strontium monohydride is produced by laser ablation of strontium dihydride in a pressurized noble gas atmosphere. The composition of the ablation plasma plume is analyzed by measuring its emission spectrum. The dynamics of SrH molecular density following the ablation laser pulse is studied as a function of the buffer gas pressure and the laser intensity.Comment: Laser Refrigeration of Solids VI, February 2 2013, San Francisco, USA, Conference Proceeding

Reconciliation of experimental and theoretical electric tensor polarizabilities of the cesium ground state

We present a new theoretical analysis of the strongly suppressed F- and M-dependent Stark shifts of the Cs ground state hyperfine structure. Our treatment uses third order perturbation theory including off-diagonal hyperfine interactions not considered in earlier treatments. A numerical evaluation of the perturbation sum using bound states up to n=200 yields ground state tensor polarizabilities which are in good agreement with experimental values, thereby bridging the 40-year-old gap between experiments and theory. We have further found that the tensor polarizabilities of the two ground state hyperfine manifolds have opposite signs, in disagreement with an earlier derivation. This sign error has a direct implication for the precise evaluation of the blackbody radiation shift in primary frequency standards.Comment: 7 pages, 2 figures, accepted for publication in Europhysics Letter

Dynamics of fine particles due to quantized vortices on the surface of superfluid 4^4He

Peculiar dynamics of a free surface of the superfluid 4He has been observed experimentally with a newly established technique utilizing a number of electrically charged fine metal particles trapped electrically at the surface by Moroshkin et al. They have reported that some portion of the particles exhibit some irregular motions and suggested the existence of quantized vortices interacting with the metal particles. We have conducted calculations with the vortex filament model, which turns out to support the idea of the vortex-particle interactions. The observed anomalous metal particle motions are roughly categorized into two types; (1) circular motions with specific frequencies, and (2) quasi-linear oscillations. The former ones seem to be explained once we consider a vertical vortex filament whose edges are terminated at the bottom and at a particle trapped at the surface. Although it is not yet clear whether all the anomalous motions are due to the quantum vortices, the vortices seem to play important roles for the motions.Comment: 7 pages, 10 figure

Zero-phonon lines in the spectra of dysprosium atoms in superfluid helium

We present an experimental study of a zero-phonon line (ZPL) in the absorption spectrum of Dy atoms solvated in superfluid He. The dopants reside in nanometer-sized spherical cavities known as atomic bubbles. We observe a temperature-dependent broadening of ZPL in the absorption spectrum. The effect is attributed to the scattering of thermal phonons on the atomic bubble that leads to the dephasing of the Dy transition dipole. The extrapolated ZPL intrinsic spectral width at zero temperature is 2300 times larger than the natural linewidth in a free atom. This can be assigned to a fast radiationless quenching of the upper state of the studied transition

Dynamics of the vortex-particle complexes bound to the free surface of superfluid helium

We present an experimental and theoretical study of the 2D dynamics of electrically charged nanoparticles trapped under a free surface of superfluid helium in a static vertical electric field. We focus on the dynamics of particles driven by the interaction with quantized vortices terminating at the free surface. We identify two types of particle trajectories and the associated vortex structures: vertical linear vortices pinned at the bottom of the container and half-ring vortices travelling along the free surface of the liquid