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Université de Fribourg

Spectroscopy of alkali-metal atoms in dense supercritical ⁴He at low temperatures

Moroshkin, Peter ; Lebedev, Victor ; Weis, Antoine

In: Physical Review A, 2013, vol. 87, no. 2, p. 022513

We present an experimental study of laser-induced fluorescence spectra of Cs atoms embedded in superfluid and solid ⁴He, as well as in dense supercritical fluid He. The studied temperature range is increased with respect to earlier studies by the use of intense laser pulses for the transient local heating of the helium sample. The analysis of the experimental spectra is based on two different...

Université de Fribourg

Laser ablation and spectroscopy of copper in liquid and solid ⁴He

Moroshkin, Peter ; Lebedev, Victor ; Weis, Antoine

In: Physical Review A - Atomic, Molecular and Optical Physics, 2011, vol. 84, no. 5, p. 052519

We present an experimental study of the laser-induced fluorescence spectra of Cu atoms in bulk liquid and solid helium matrices as well as in the dense plasma created by the laser ablation of copper in liquid helium. We observe transitions of the valence electron and of inner-shell electrons. The former produce structureless line shapes, a large broadening, and a blueshift. The latter practically...

Université de Fribourg

Phonon generation in condensed ⁴He by laser-excited atomic bubbles

Moroshkin, Peter ; Lebedev, Victor ; Weis, Antoine

In: Europhysics Letters, 2011, vol. 96, no. 2, p. 26002

We discuss the interaction between nanometer-sized defects (atomic bubbles) and elementary excitations (phonons) in quantum fluids and solids. We observe that optical excitations in embedded metal atoms induce bubble expansions/contractions that create strongly localized phonon wave packets in the quantum matrix. We derive the structure and dynamics of these vibronic excitations from the...

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

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

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

Nanowire formation by gold nano-fragment coalescence on quantized vortices in He II

Moroshkin, Peter ; Lebedev, Victor ; Grobéty, Bernard ; Neururer, Christoph ; Gordon, E. B. ; Weis, Antoine

In: Europhysics Letters, 2010, vol. 90, no. 3, p. 34002

We demonstrate that laser ablation of a gold target immersed in superfluid and normal fluid helium leads to the formation of elongated gold nano-fragments. In the superfluid phase these nano-fragments aggregate into filaments with extremely large aspect ratios displaying metallic electric conductivity. We attribute this unusual structure to the coalescence of gold particles trapped on quantized...

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

Positive Ion Induced Solidification of ⁴He

Moroshkin, Peter ; Lebedev, Victor ; Weis, Antoine

In: Physical Review Letters, 2009, vol. 102, no. 11, p. 115301

We have observed bulk solidification of ⁴He induced by nucleation on positive alkali ions in pressurized superfluid helium. The ions are extracted into the liquid from alkali-doped solid He by a static electric field. The experiments prove the existence of charged particles in a solid structure composed of doped He that was recently shown to coexist with superfluid helium below the He...

Université de Fribourg

Lifetime studies of Cs*HeN exciplexes in solid ⁴He

Moroshkin, Peter ; Hofer, Adrian ; Lebedev, Victor ; Weis, Antoine

In: Physical Review A, 2008, vol. 78, p. 032501

We present time-resolved measurements of the laser-induced fluorescence from Cs atoms and Cs*HeN exciplexes in a solid ⁴He matrix. The linear Cs*He₌₂ exciplex is strongly quenched by a radiationless transformation into a ring-shaped Cs*HeN=6,7 exciplex, which decays radiatively with a lifetime of 88±2 ns. The analysis...