A. Weis

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

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 vortices. Our observations suggest new ways to visualize the structure of quantized vortex bundles and a new approach for producing centimeter-long metal nanowires.

Pressure shift of atomic resonance lines in liquid and solid helium

We show that for atoms trapped in a liquid He matrix the excitation and emission spectra can be quantitatively described by the bubble model which treats the matrix as an incompressible continuous medium. Comparison with experimental results shows that the model also holds for a solid matrix. The model is only valid in the case where the attractive He−He interaction dominates the attractive part of the foreign atom-helium interaction. Its failure in the case of implanted Na atoms is discussed.

Can paramagnetic atoms in superfluid helium be used to search for permanent electric dipole moments

Abstract Large densities together with long trapping times have been observed for atoms immersed in He II. The feasibility of experiments searching for permanent electric dipole moments (PEDM) of paramagnetic atoms in He II is discussed.

Implantation and spectroscopy of metal atoms in solid helium

The first implantation of neutral Ba and Cs atoms into solid4He is reported. We discuss details of the experimental setup and techniques used to load the helium with atoms at concentrations of 108 cm−3. If photodissociation of Cs molecules and clusters is performed twice per hour this atomic concentration can be kept without a second implantation for almost a day. From the optical spectra of Ba in solid helium we infer no significant difference in the trapping site with respect to that in liquid helium.

Quantitative interpretation of the nonlinear Faraday effect as a Hanle effect of a light-induced birefringence

We present a simple quantitative description of the lowest-order nonlinear Faraday effect of an atomic vapor by modeling the effect as a Hanle-type precession of the quadrupole moment induced by optical pumping. This gives the medium the symmetry of uniaxial birefringence, and the Faraday rotation is expressed in terms of this birefringence. We obtain expressions for transitions between states of arbitrary angular momenta; the new expressions match results obtained earlier for the case of depopulation pumping. The novel aspects are that only level populations intervene and that no explicit use of sublevel coherences is made. We present experimental verifications of the equivalence of light-induced birefringence and the nonlinear Faraday effect.

Observation of Ramsey fringes in nonlinear Faraday rotation

Abstract The evolution of Δm = 2 ground state coherences was investigated in a thermal Rb atomic beam using spatially separated laser beams. The coherence was created by optical pumping with a linearly polarized light beam and was probed, after evolving in a homogeneous magnetic field via the rotation of the plane of polarization of a second light beam. The observed signal shows dispersively shaped Ramsey fringes with a fringe width of 6 kHz.

Time of flight effects in nonlinear magneto-optical spectroscopy

Abstract Due to time-of-flight effects the line-shapes of dark/bright absorption resonances and of the magneto-rotation spectrum (non-linear Faraday effect) observed in the forward scattering of resonance radiation in alkali vapors differ from absorptive and dispersive lorentzians. We present a simple model which takes the finite interaction time of vapor atoms with a gaussian laser beam into account and compare the theoretical results with experimental data obtained on the Cs D2 line.

Spin physics in solid helium: Experimental results and applications

We have observed optical pumping signals from Cs atoms trapped in solid4He. While the longitudinal electronic spin relaxation timeT1 is found to be in the range of 1–2 s, the transverse relaxation timeT2, as inferred from magnetic resonance linewidths has a lower bound of 150 μs, and is determined by magnetic field inhomogeneities. We present a quantitative discussion of how paramagnetic species trapped in solid He might be used in a highly sensitive search for permanent atomic electric dipole moments.

The Hyperfine Structure of Cs Atoms in the b.c.c. Phase of Solid 4He

We have detected the ground state F = 4 → F = 3 hyperfine transition of cesium atoms implanted in a b.c.c. matrix of solid 4He using a microwave-optical double-resonance technique. The transition frequency is blue-shifted by ~ 197 MHz (2.1%) with respect to the free atomic transition and grows with increasing pressure at a rate of ~ 1.4 MHz/bar.

A single mode, cw, diode laser at the cesium D1 (894.59 nm) transition

Abstract We demonstrate that the C86135E/C86136E series laser diodes from EG&G Optoelectronics can be operated at the cesium D 1 line with grating feedback. For a free running power of 46 mW, we achieved 36 mW of single mode power.