Université de Fribourg

Rb*Hen exciplexes in solid ⁴He

Hofer, Adrian ; Moroshkin, Peter ; Nettels, Daniel ; Ulzega, Simone ; Weis, Antoine

In: Physical Review A, 2006, vol. 74, p. 032509

We report the observation of emission spectra from Rb*Hen 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...

Université de Fribourg

6S1/2-6P1/2 transition of Cs atoms in cubic and hexagonal solid ⁴He

Hofer, Adrian ; Moroshkin, Peter ; Ulzega, Simone ; Nettels, Daniel ; Müller-Siebert, Reinhard ; Weis, Antoine

In: Physical Review A, 2007, vol. 76, no. 2, p. 022502

We present a systematic experimental study of the absorption and fluorescence spectra of the 6S1/2-6P1/2 transition in Cs atoms isolated in solid ⁴He matrices. The bubble model developed earlier for alkali-metal atoms in liquid He is revised and applied to the present system. The analysis of the dependencies of absorption and fluorescence wavelengths on He...

Université de Fribourg

Calculation of the forbidden electric tensor polarizabilities of free Cs atoms and of Cs atoms trapped in a solid ⁴He matrix

Hofer, Adrian ; Moroshkin, Peter ; Ulzega, Simone ; Weis, Antoine

In: Physical Review A, 2008, vol. 77, no. 12, p. 012502

We give a detailed account on our semiempirical calculations of the forbidden electric tensor polarizability α₂⁽³⁾ of the ground state of free Cs atoms and of Cs atoms implanted in a solid 4He matrix. The results are compared with measurements of α₂⁽³⁾ in the free atoms [Europhys. Lett. 76, 1074 (2006)] and in He-trapped atoms [Phys. Rev. A 75, 042505 (2007)]. Features with...

Université de Fribourg

Lifetime of the Cs 6P1/2 state in bcc and hcp solid ⁴He

Hofer, Adrian ; Moroshkin, Peter ; Ulzega, Simone ; Weis, Antoine

In: The European Physical Journal D, 2008, vol. 46, no. 1, p. 9-14

We present the first experimental study of time-resolved fluorescence from laser-excited Cs(6P1/2) atoms isolated in a solid ⁴He matrix. The results are compared to the predictions of the bubble model including the interaction of the atomic dipole with its radiation reflected at the bubble interface. Our results show that in liquid He as well as in the body-centered cubic (bcc)...

Université de Fribourg

Atomic bubbles in impurity-stabilized solid ⁴He

Lebedev, Victor ; Moroshkin, Peter ; Weis, Antoine

In: Fizika Nizkikh Temperatur, 2010, vol. 35, no. 4, p. 391-395

The optical absorption and fluorescence spectra of alkali atoms isolated in liquid and solid He matrices depend on specific macroscopic matrix properties, such as their molar volume and (anisotropic) elasticity constants, and provide thus information about the quantum matrix. We have applied optical spectroscopy to investigate the properties of a recently discovered impurity-stabilized doped...

Université de Fribourg

Spectroscopy of barium atoms in liquid and solid helium matrices

Lebedev, Victor ; Moroshkin, Peter ; Weis, Antoine

In: Physical Review A - Atomic, Molecular and Optical Physics, 2011, vol. 84, no. 2, p. 022502

We present an exhaustive overview of optical absorption and laser-induced fluorescence lines of Ba atoms in liquid and solid helium matrices in visible and near-infrared spectral ranges. Due to the increased density of isolated atoms, we have found a large number of spectral lines that were not observed in condensed helium matrices before. We have also measured the lifetimes of metastable states....

Université de Fribourg

Spectroscopy of nonspherical atomic bubbles in solid Helium

Lebedev, Victor ; Moroshkin, Peter ; Weis, Antoine

In: The Journal of Physical Chemistry A, 2011, vol. 115, no. 25, p. 7169–7179

We analyze the effect of the host crystal symmetry on the optical spectra of the 6P1/2−6S1/2 and 6P3/2−6S1/2 transitions of atomic Cs in solid ⁴He matrices. In particular, we address the deformation of the bubble structures formed by Cs in such quantum crystals. We show that the anisotropy of the stiffness tensor leads...

Université de Fribourg

Formation of metallic nanowires by laser ablation in liquid Helium

Lebedev, Victor ; Moroshkin, Peter ; Grobéty, Bernard ; Gordon, Eugene ; Weis, Antoine

In: Journal of Low Temperature Physics, 2011, vol. 165, no. 3-4, p. 166-176

Laser ablation of metals in liquid helium results in the formation of metal filaments with diameters on the order of 2–10 nanometres and of spherical nanoparticles. In superfluid helium these nanowires aggregate into centimeter-sized networks. We study the morphology and the electric conductivity of these large aggregates, as well as extinction spectra and the crystalline structure of the...

Université de Fribourg

Atomic and molecular defects in solid ⁴He

Moroshkin, Peter ; Hofer, Adrian ; Weis, Antoine

In: Physics Reports, 2008, vol. 469, no. 1, p. 1-57

The studies of defects formed by impurity particles (atoms, molecules, exciplexes, clusters, free electrons, and positive ions) embedded in liquid and solid ⁴He are reviewed. The properties of free electrons and neutral particles in condensed helium are described by the electron (atomic) bubble model, whereas for the positive ions a snowball structure is considered. We compare the properties of...