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PubMed2000

Cold rubidium molecules formed in a magneto-optical trap

We report the first observation of translationally cold ( approximately 90 &mgr;K) Rb2 molecules. They are produced in a magneto-optical trap in their triplet ground state. The detection is performed by selective mass spectroscopy after two-photon ionization into Rb+2, resonantly enhanced through the intermediate a (3)Sigma(+)(u)-->2 (3)Pi(g) molecular band. The two rubidium isotopes present very different types of behavior that are interpreted in terms of their respective collisional properties.

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PubMed2000

Determination of cross sections and continuum phases of rubidium through complete measurements of atomic multiphoton ionization

We present a complete experimental determination of the atomic parameters necessary to unambiguously characterize two-photon ionization of atomic rubidium, i.e., the relative photoionization cross sections and the continuum wave function phase difference. We obtain these complete results through a single measurement, that of the two-photon photoelectron angular distribution using elliptically polarized light. While measured phase differences are in excellent agreement with expected values, the ratios of photoionization cross sections of the two D channels are not.

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PubMed2004

Observation of light dragging in a rubidium vapor cell.

We report on the experimental demonstration of the light dragging effect due to atomic motion in a rubidium vapor cell. We find that the minimum group velocity is achieved for light redshifted from the center of the atomic resonance and that the value of this shift increases with decreasing group velocity, in agreement with the theoretical predictions by Kocharovskaya, Rostovtsev, and Scully [Phys. Rev. Lett. 86, 628 (2001)].

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PubMed2005

Quantum-degenerate mixture of fermionic lithium and bosonic rubidium gases.

We report on the observation of sympathetic cooling of a cloud of fermionic 6Li atoms which are thermally coupled to evaporatively cooled bosonic 87Rb. Using this technique we obtain a mixture of quantum-degenerate gases, where the Rb cloud is colder than the critical temperature for Bose-Einstein condensation and the Li cloud is colder than the Fermi temperature. From measurements of the thermalization velocity we estimate the interspecies s-wave triplet scattering length |amx|=20(+9)(-6)aB. We found that the presence of residual rubidium atoms in the |2, 1> and the |1, -1> Zeeman substates gives rise to important losses due to inelastic collisions.

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PubMed2006

Low-light-level optical interactions with rubidium vapor in a photonic band-gap fiber.

We show that rubidium vapor can be produced within the core of a photonic band-gap fiber yielding an optical depth in excess of 2,000. Our technique for producing the vapor is based on coating the inner walls of the fiber core with organosilane and using light-induced atomic desorption to release Rb atoms into the core. As an initial demonstration of the potential of this system for supporting ultralow-level nonlinear optical interactions, we perform electromagnetically induced transparency with control-field powers in the nanowatt regime, which represents more than a 1,000-fold reduction from the power required for bulk, focused geometries.

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PubMed1966

Ion Absorption and Retention by Chlorella Pyrenoidosa. II. Permeability of the Cell to Sodium and Rubidium.

The Na and Rb permeability of Chlorella pyrenoidosa were estimated from the rates of radioisotope self-diffusion.The isotopic exchange in absence of net ionic movements followed first order kinetics. This suggested that for sodium, which reached isotopic equilibrium in approximately 90 minutes, the cell behaved as 1 compartment with respect to isotopic exchange. Rubidium in 180 minutes approached isotopic equilibrium by 67%; thus, the existence of a single compartment for Rb has not been demonstrated. Net fluxes, calculated from the isotope exchange data, and expressed on a dry weight and surface area base showed that Na fluxes were approximately 7 times larger than Rb fluxes. Net Na fluxes of 90 milli-equivalents per 100 g dry weight per hour were far in excess of the observed maximum net accumulation of Na. However, Rb fluxes of 13 milliequivalents per 100 g dry weight per hour were of similar magnitude as the rate of Rb accumulation. Thus, permeability could be a limiting factor for Rb but not for Na accumulation. Sodium and Rb fluxes in absence of net ionic movements were inhibited by low temperature, dark air and dark N(2) conditions. This change in flux rates was explained mainly on the basis of metabolically dependent changes in the cell surface layers.Isotope fluxes of Rb were drastically reduced in dark air and dark N(2) in the absence or presence of net cation movements. Dark N(2) essentially eliminated net cation accumulation, whereas dark air had relatively little effect on the net K and Rb accumulation by Chlorella. Thus the 2 major factors involved in net cation accumulation in the Chlorella cell, permeability and processes leading to cation retention, respond differently to metabolic inhibition permitting a separation of these 2 important aspects of cation accumulation.

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PubMed1970

Interactions of rubidium, sodium, and potassium on the nutrition of sugar beet plants.

The effect of Rb on the growth and the development of sugar beet plants (Beta vulgaris, var. MS NB1 x NB4) depends on the Rb concentration, the K supply, and the relative abundance of Na. Rubidium added either to a low or high K solution with or without added Na increased leaf blade size greatly, possibly through an effect on phytohormones or through a "partitioning effect" on the distribution of carbohydrates, with top growth favored over storage roots.Sodium increased the growth of sugar beet plants when they were either K-deficient or adequately supplied with K. Sodium or Rb added to a high K solution increased the sucrose percentage and total sucrose of the storage roots significantly. Sodium and Rb supplied simultaneously to the nutrient solution resulted in synergetic effects only at low K supply.Potassium was translocated in mature leaves from the petiole to the blade when Na was added to a low K solution, or when Rb was added either to a low or a high K solution. Rb + K had little to no effect on Na redistribution.

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PubMed1980

Cortical Air Spaces (Aerenchyma) in Roots of Corn Subjected to Oxygen Stress: STRUCTURE AND INFLUENCE ON UPTAKE AND TRANSLOCATION OF RUBIDIUM IONS.

When the seminal root system of 14-day-old corn (Zea mays cv. Dekalb 202) was subjected to O(2) stress, nodal roots with well developed cortical air spaces (aerenchyma) grew into the deoxygenated solution. Microscopic examination showed that there was extensive breakdown of cells in the midcortex of these roots, while the stele, endodermis, and inner layer of cortical cells remained complete, as did the outer layers of the cortex and the epidermis. Occasional files of intact cells, and the wall residues of collapsed cells, crossed the space between inner and outer cortex. Experiments with short, intact root segments with and without air spaces showed that in the presence of O(2) the ability to absorb and translocate (86)Rb(+), per unit volume or length of root, was little affected by cortical degeneration. The distribution across root sections of recently supplied strontium and rubidium, determined by electron microprobe analysis, indicated that in roots with air spaces the strands of wall residues bridging the cortex could be involved in maintaining the conduction of ions from the outer cortex up to the endodermis.

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PubMed2004

Rubidium metaborate, Rb3B3O6.

Rubidium metaborate, Rb3B3O6, was obtained by the reaction of Rb2CO3 and BN using a radiofrequency furnace at a maximum reaction temperature of 1173 K. The crystal structure has been determined by single-crystal X-ray diffraction. The space group is R3c, with all atoms positioned on a twofold axis (Wyckoff site 18e). The ionic compound is isotypic with Na3B3O6, K3B3O6 and Cs3B3O6.

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PubMed2005

Rubidium gadolinium bis(tungstate).

The structure of rubidium gadolinium bis(tungstate), RbGd(WO4)2, has been determined. The crystal is built up from corner- and edge-sharing WO6 octahedral and GdO8 polyhedral groups, giving rise to a Gd-WO4 polyhedral backbone surrounding structural cavities filled with Rb+ cations. The Gd and Rb atoms lie on twofold axes.

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PubMed2006

A new rubidium beryllium borate, RbBe4(BO3)3.

Single crystals of a new rubidium beryllium borate, RbBe4(BO3)3, have been obtained by spontaneous nucleation from a high-temperature melt. This new orthorhombic (Pnma) structure type contains [Be2BO4]- rings, made of two BeO4 tetrahedra and one BO3 triangle, which constitute the basic structural units. The m plane runs through the B and one of the O atoms and intersects the ring. These rings form chains in the a direction, which are connected in the b and c directions to form zeolite-type cages in which the Rb+ cations are located, at sites of m symmetry.

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PubMed2006

Rubidium dimolybdate, Rb(2)Mo(2)O(7), and caesium dimolybdate, Cs(2)Mo(2)O(7).

The crystal structures of dirubidium heptaoxodimolybdate, Rb(2)Mo(2)O(7), and dicaesium heptaoxodimolybdate, Cs(2)Mo(2)O(7), in the space groups Ama2 and P2(1)/c, respectively, have been determined for the first time by single-crystal X-ray diffraction. The structures represent two novel structure types of monovalent ion dimolybdates, A(2)Mo(2)O(7) (A = alkaline elements, NH(4), Ag or Tl). In the structure of Rb(2)Mo(2)O(7), Mo atoms are on a twofold axis, on a mirror plane and in a general position. One of the Rb atoms lies on a twofold axis, while three others are on mirror planes. Two O atoms attached to the Mo atom on a mirror plane are located on the same plane. Rubidium dimolybdate contains a new kind of infinite Mo-O chain formed from linked MoO(4) tetrahedra and MoO(6) octahedra alternating along the a axis, with two terminal MoO(4) tetrahedra sharing corners with each octahedron. The chains stack in the [001] direction to form channels of an approximately square section filled by ten-coordinate Rb ions. Seven- and eight-coordinate Rb atoms are located between chains connected by a c translation. In the structure of Cs(2)Mo(2)O(7), all atoms are in general positions. The MoO(6) octahedra share opposite corners to form separate infinite chains running along the c axis and strengthened by bridging MoO(4) tetrahedra. The same Mo-O polyhedral chain occurs in the structure of Na(2)Mo(2)O(7). Eight- to eleven-coordinate Cs atoms fill the space between the chains. The atomic arrangement of caesium dimolybdate has an orthorhombic pseudosymmetry that suggests a possible phase transition P2(1)/c-->Pbca at elevated temperatures.

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PubMed2005

Does the light shift drive frequency aging in the rubidium atomic clock?

Frequency aging in the rubidium (Rb) vapor-cell atomic clock plays a significant role in the device's timekeeping ability. Though many researchers have speculated on the physical mechanism(s) driving the linear, deterministic frequency change (i.e., deltaf(t)/fo = At), there is little unambiguous experimental data regarding the phenomenon. Here, long-term data were used from on-orbit global positioning system (GPS) Rb clocks to examine one postulated mechanism for frequency aging (i.e., the light-shift effect). Defining the light shift of the clock's fractional frequency as alphaI/Io, where alpha is the light-shift coefficient, we find that temporal variations of the relative light intensity, I/Io, cannot account for frequency aging. However, for the population of clocks considered here, we obtain the intriguing result that alpha/A = 1.7 +/- 1.5. Thus, it may be that frequency aging is driven by the light-shift effect through temporal variations of the light-shift coefficient.

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PubMed2006

The pulsed rubidium clock.

In this paper, we describe a laboratory prototype of pulsed optically pumped clock based on a rubidium vapor cell with buffer gas. The measured frequency stability (overlapping Allan deviation) is sigma(y)(tau) = 3 x 10(-12)tau(-1/2) and the level of 4 x 10(-14) is reached for averaging time of r = 3 x 10(14) s. For the same set of data, the statistical tool Theol predicts a frequency stability of 2 x 10(-14) for tau = 10(5) s. This result confirms the theoretical predictions regarding this kind of frequency standard and makes it very attractive for satellite navigation and space applications in which a simple and reliable implementation is required, and the short and medium term stability (till one day) is the main concern.

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PubMed2005

All-optical switching in rubidium vapor.

We report on an all-optical switch that operates at low light levels. It consists of laser beams counterpropagating through a warm rubidium vapor that induce an off-axis optical pattern. A switching laser beam causes this pattern to rotate even when the power in the switching beam is much lower than the power in the pattern. The observed switching energy density is very low, suggesting that the switch might operate at the single-photon level with system optimization. This approach opens the possibility of realizing a single-photon switch for quantum information networks and for improving transparent optical telecommunication networks.

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PubMed2006

Rubidium-rich asymptotic giant branch stars.

A long-debated issue concerning the nucleosynthesis of neutron-rich elements in asymptotic giant branch (AGB) stars is the identification of the neutron source. We report intermediate-mass (4 to 8 solar masses) AGB stars in our Galaxy that are rubidium-rich as a result of overproduction of the long-lived radioactive isotope (87)Rb, as predicted theoretically 40 years ago. This finding represents direct observational evidence that the (22)Ne(alpha,n)(25)Mg reaction must be the dominant neutron source in these stars. These stars challenge our understanding of the late stages of the evolution of intermediate-mass stars and would have promoted a highly variable Rb/Sr environment in the early solar nebula.

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PubMed2004

Frequency locking of tunable diode lasers to a rubidium-stabilized ring-cavity resonator.

We demonstrate a technique for locking the frequency of a tunable diode laser to a ring-cavity resonator. The resonator is stabilized to a diode laser that is in turn locked to an atomic transition in rubidium, thus giving it absolute frequency calibration. The principal advantage of the ring-cavity design is that there is no feedback destabilization of the laser. The cavity has a free-spectral range of 1.3 GHz and Q of approximately 35, which provides robust locking of the laser. The locked laser is able to track large scans of the cavity.

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