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

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

Spectroscopy of Rb2_{2} dimers in solid 4^{4}He

We present experimental and theoretical studies of the absorption, emission and photodissociation spectra of Rb$_{2}$ molecules in solid helium. We have identified 11 absorption bands of Rb$_{2}$. All laser-excited molecular states are quenched by the interaction with the He matrix. The quenching results in efficient population of a metastable (1)$^{3}\Pi_{u}$ state, which emits fluorescence at 1042 nm. In order to explain the fluorescence at the forbidden transition and its time dependence we propose a new molecular exciplex Rb$_{2}(^{3}\Pi_{u})$He$_{2}$. We have also found evidence for the formation of diatomic bubble states following photodissociation of Rb$_{2}$

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

Abstract.: 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) crystalline phase of He the lifetime of excited Cs atoms does not depend on He pressure, in agreement with our theory. When going from the bcc to the hexagonally close-packed (hcp) phase of 4He the lifetime is reduced by ≈10% and decreases further with increasing He pressure. We assign this effect to the formation of Cs*Hen exciplexes, and determine the pressure dependence of the probability that the 6P1/2 state decays via this nonradiative channe

Discovery of dumbbell-shaped Cs*He_n exciplexes in solid He 4

We have observed several new spectral features in the fluorescence of cesium atoms implanted in the hcp phase of solid helium following laser excitation to the 6$^{2}$P states. Based on calculations of the emission spectra using semiempirical Cs-He pair potentials the newly discovered lines can be assigned to the decay of specific Cs*He$_{n}$ exciplexes: an apple-shaped Cs$(A\Pi _{3/2})$He$_{2}$ and a dumbbell-shaped Cs$(A\Pi_{1/2})$He$_{n}$ exciplex with a well defined number $n$ of bound helium atoms. While the former has been observed in other enviroments, it was commonly believed that exciplexes with $n>2$ might not exist. The calculations suggest Cs$(A\Pi_{1/2})$He$_{6}$ to be the most probable candidate for that exciplex, in which the helium atoms are arranged on a ring around the waist of the dumbbell shaped electronic density distribution of the cesium atom.Comment: 4 pages, 4 figure

Multi-photon processes in the Zeeman structure of atomic Cs trapped in solid helium

We report magnetic resonance experiments with optical detection performed on cesium atoms trapped in a crystalline Hematrix. Multi-photon transitions, i.e., processes in which several radio-frequency photons are absorbed simultaneously in a given hyperfine Zeeman multiplet of the ground state, were the central topic of these studies. The long relaxation times of spin coherences of Cs in solid He allow such transitions to be spectrally resolved in fields as low as 1mT. We observed all allowed multi-photon transitions up to the ΔM=8 transition in the F=4 state. We compare the experimental spectra with theoretical spectra obtained from numerical solutions of the Liouville equation that include optical pumping and the interaction with the static and oscillating fields. Multi-photon transitions may find applications in magnetometry, suppress systematic effects in EDM experiments, and allow the study of relaxation phenomena in doped He crystals. The demonstration of these features is still hindered by inhomogeneous line broadenin

Spectroscopy of atomic and molecular defects in solid ⁴He using optical, microwave, radio frequency, magnetic and electric fields (Review Article)

A little more than a decade ago our team extended the field of defect spectroscopy in cryocrystals to solid ⁴He matrices, in both their body-centered cubic (bcc) and hexagonally close-packed (hcp) configurations. In this review paper we survey our pioneering activities in the field and compare our results to those obtained in the related fields of doped superfluid helium and doped helium nanodroplets, domains developed in parallel to our own efforts. We present experimental details of the sample preparation and the different spectroscopic techniques. Experimental results of purely optical spectroscopic studies in atoms, exciplexes, and dimers and their interpretation in terms of the so-called bubble model will be discussed. A large part of the paper is devoted to optically detected magnetic resonance, ODMR, processes in alkali atoms. The quantum nature of the helium matrix and the highly isotropic shape of the local trapping sites in the bcc phase make solid helium crystals ideal matrices for high resolution spin physics experiments. We have investigated the matrix effects on both Zeeman and hyperfine magnetic resonance transitions and used ODMR to measure the forbidden electric tensor polarizability in the ground state of cesium. Several unexpected changes of the optical and spin properties during the bcc—hcp phase transition can be explained in terms of small bubble deformations

Late Quaternary sea-level change and early human societies in the central and eastern Mediterranean Basin : an interdisciplinary review

This article reviews key data and debates focused on relative sea-level changes since the Last Interglacial (approximately the last 132,000 years) in the Mediterranean Basin, and their implications for past human populations. Geological and geomorphological landscape studies are critical to archaeology. Coastal regions provide a wide range of resources to the populations that inhabit them. Coastal landscapes are increasingly the focus of scholarly discussions from the earliest exploitation of littoral resources and early hominin cognition, to the inundation of the earliest permanently settled fishing villages and eventually, formative centres of urbanisation. In the Mediterranean, these would become hubs of maritime transportation that gave rise to the roots of modern seaborne trade. As such, this article represents an original review of both the geo-scientific and archaeological data that specifically relate to sea-level changes and resulting impacts on both physical and cultural landscapes from the Palaeolithic until the emergence of the Classical periods. Our review highlights that the interdisciplinary links between coastal archaeology, geomorphology and sea-level changes are important to explain environmental impacts on coastal human societies and human migration. We review geological indicators of sea level and outline how archaeological features are commonly used as proxies for measuring past sea levels, both gradual changes and catastrophic events. We argue that coastal archaeologists should, as a part of their analyses, incorporate important sea-level concepts, such as indicative meaning. The interpretation of the indicative meaning of Roman fishtanks, for example, plays a critical role in reconstructions of late Holocene Mediterranean sea levels. We identify avenues for future work, which include the consideration of glacial isostatic adjustment (GIA) in addition to coastal tectonics to explain vertical movements of coastlines, more research on Palaeolithic island colonisation, broadening of Palaeolithic studies to include materials from the entire coastal landscape and not just coastal resources, a focus on rescue of archaeological sites under threat by coastal change, and expansion of underwater archaeological explorations in combination with submarine geomorphology. This article presents a collaborative synthesis of data, some of which have been collected and analysed by the authors, as the MEDFLOOD (MEDiterranean sea-level change and projection for future FLOODing) community, and highlights key sites, data, concepts and ongoing debates