Laser-cooling effects in few-ion clouds of Yb+

We report some laser-cooling effects in a few¹⁷²Yb⁺ ions held in a Paul trap. Pronounced cloud-to-crystal phase transitions have been observed as discontinuities in the Yb⁺ fluorescence spectrum of the 369 nm cooling transition. The first reported two-dimensional images of Yb⁺ clouds with evidence of crystal structure have been recorded using a photon-counting position-sensitive detector. An ion temperature of 100 mK has been estimated from the size of a single ion image. Step-wise cooling of a re-heated, few-ion Yb⁺ cloud was also observed.     

Spatial variability of 2H and 18O composition of meteoric freshwater lakes in Scotland

Coastal regions, and in particular islands where precipitation from clouds formed out at sea occurs for the first time, are prime candidates for regions where ²H and ¹⁸O composition of precipitation will deviate significantly from the global mean geographic and physiographic trends of vapour-transport patterns. The results reported here are the outcome of a study that aimed to test this hypothesis by ‘isotopographically’ mapping the characteristic δ²H and δ¹⁸O signatures of Scottish freshwaters. The resulting isotope abundance landscapes or ‘isoscapes’ will underpin studies aiming to authenticate origin of Scottish produce but may also offer a baseline against which environmental changes could be assessed. Between April 2011 and May 2012 freshwater samples were collected from 127 different freshwater lochs and reservoirs across Scotland, and analysis results were compared to precipitation data provided by the British Geological Survey. Here we present the results of the ²H and ¹⁸O analyses of these water samples as well as the first detailed Scotland freshwater isoscapes with a grid resolution of about 5 × 5 km (0.05 degrees).     

Measurement of K absorption edge energies of silver and tin targets using a weak beta source

K absorption edge energies of Ag and Sn elements have been determined by using a weak beta source. In this method, the beta particles from a ⁹⁰Sr? ⁹⁰Y beta source interact with an iron foil to produce the external bremsstrahlung (EB) photons. The spectrum of EB photons is passed through the elemental target and the spectrum of transmitted photons is recorded with a high resolution HPGe detector spectrometer coupled to 16K multichannel analyzer. The recorded transmitted EB spectrum shows a sharp decrease in intensity at the K shell binding energy of elemental target. Such a sharp decrease region, which is corrected for Kβ′₂ contribution, has been used to determine the K absorption edge energies of Ag and Sn elemental targets. The measured values have been compared with theoretical and experimental values. Copyright © 2010 John Wiley & Sons, Ltd.     

A wide angle neutron spin filter system using polarized He

Polarized ³He neutron spin filters can operate over a wide neutron energy range and provide a large angular acceptance. A compact ³He neutron spin filter system has been developed for the Multi-Axis Crystal Spectrometer at the National Institute of Standards and Technology (NIST) Center for Neutron Research. Sealed ³He cells, polarized by spin-exchange optical pumping, are used as polarizer and analyzer. The polarization of the neutrons incident on the sample is inverted by flipping the polarization of the ³He gas in the polarizer, with only a small effect on the analyzer cells. The cell fabrication process, ³He spin flipper, and the holding magnetic field are discussed and we present the results of a first on-linetest.     

The synthesis of organic molecules in a laser plasma similar to the plasma that emerges in hypervelocity collisions of matter at the early evolutionary stage of the Earth and in interstellar clouds

Ions of organic molecules and polymers as well as multiply ionized hydrocarbons were synthesized and detected with a time-of-flight mass analyzer in laboratory experiments simulating with a laser the plasma processes that accompany a hypervelocity micrometeorite impact on the target surface. A hypervelocity impact of micrometeorites moving at velocities of 80 km s^?1 on a inorganic target was simulated with a Q-switched laser. The laser provided a power density of 10⁹?10¹¹ W cm^?2 in a spot with an impact diameter of 30–150 μm for a pulse duration of 7–10 ns and a laser plasma electron density of 10⁵?10⁶ K. The ions of organic compounds are shown to be synthesized mostly during the free expansion of a hot laser plasma at the stage of its cooling and recombination if, initially, the plasma was completely atomized and ionized. Molecular ions have high yields only for a carbon target. The results obtained indicate that organic or other polyatomic compounds can be abiogenically synthesized in intense hypervelocity meteorite impacts on the Earth’s surface at the early stage of its formation during meteorite showers and in hypervelocity collisions of dust particles in interstellar molecular clouds.     

A high-sensitivity laser microprobe mass analyzer

A laser microprobe mass analyzer has been developed. It is intended for application in biomedical and physiological research. A frequency-doubled ruby laser is focussed through an incident light microscope to a spot of minimally 0.5 μm in diameter on a thin section specimen of 0.1–1.5 μm thickness. The microplasma generated from the irradiated volume is analyzed in a time-of-flight mass spectrometer recording the complete spectrum for each shot. From lithium doped epoxy resin (5 ppm by weight), used as an organic standard, 1.4×10⁻¹⁹g or 1.4×10⁴ atoms of the⁶Li isotope have been detected. This sensitivity corresponds to that of ion microprobes but is at least an order of magnitude higher than obtained with electron probe X-ray microanalyzers.     

A double Paul trap system for the electronic coupling of ions

We report on the progress towards the implementation of a double trap system for the coupling of ion clouds stored in different traps through the charges they induce in a common electrode. The two traps have cylindrical symmetry and can be used either as Penning or Paul traps. The laser system for Doppler cooling of ⁴⁰Ca⁺ clouds is described. The cooling can be performed differentially in the two traps, aiming at the study of the coupling between two clouds of ions at different temperatures. This setup is the starting point for the realization of energy transfer between two Doppler-cooled ions stored in different traps. We report on the status of the experiment and evaluate the performance required for an efficient coupling.     

Absolutbestimmung der austrittsarbeit von palladium mit einem röntgenphotoelektronenspektrometer

Based on the work of Ascarelli and Missoni⁴ and Evans¹ a method for absolute measurements of work-functions of electrically conductive samples is developed which is applicable to instruments without retarding field and with a spherical analyzer. The calibration of the instrument, as well as the determination of the onset of the secondary electron spectrum and the Fermi-level, are discussed. For a polycrystalline palladium platelet with an argon-ion cleaned surface, a work-function ofW′_Pd = 4.5(4) ± 0.2(0) eV has been obtained, which agrees with the literature value³ of 4.64 eV within the range of accuracy.     

The ν19a band of fluorobenzene

The high-resolution infrared spectrum of the ν_19a band of fluorobenzene has been recorded near 1500 cm⁻¹. Fluorobenzene was cooled to ca. 25 K in a jet expansion with He. A tunable diode laser was used as excitation source, and a multipass system was employed. The spectrum shows groupings of lines in the P and R regions, similar to pseudo Q branches. The analysis of the spectrum yields accurate values for the band origin, rotational constants, and the off-diagonal quadratic centrifugal distortion constants.     

Study of the K shell photoelectric parameters of Dy,Yb and W atoms using low energy bremsstrahlung radiation

Low energy external bremsstrahlung (EB) photons were used to estimate the K shell photoelectric parameters; the K shell photoelectric cross section at the K edge, the K shell binding energy, the K shell jump ratio, the K shell jump factors, the Davisson-Kirchner ratio and the K shell oscillator strength for dysprosium (Dy), ytterbium (Yb) and tungsten (W) atoms. The EB photons are produced in the nickel (Ni) target by using the beta particles from a weak beta source of ⁹⁰Sr–⁹⁰Y. These photons are made to fall on these elemental targets of our interest and the transmitted spectrum is measured using GMX 10P HPGe detector coupled to an 8K multichannel analyzer. The sharp decrease at the K edge in the measured spectrum is used to determine the K shell photoelectric parameters of these elements. The experimental results are in good agreement with the theoretical values.     

Development of high vorticity in incompressible 3D Euler equations: Influence of initial conditions

The incompressible three-dimensional ideal flows develop very thin pancake-like regions of increasing vorticity. These regions evolve with the scaling ω_max(t) ∝ l(t)^-2/3 between the vorticity maximum and pancake thickness, and provide the leading contribution to the energy spectrum, where the gradual formation of the Kolmogorov interval E _k ∝ k^?5/3 is observed for some initial flows. With the massive numerical simulations, we study the influence of initial conditions on the processes of pancake formation and the Kolmogorov energy spectrum development.     

Optical fiber-based gamma-ray spectroscopy with cerium-doped lutetium yttrium orthosilicate crystal

A fiber-optic radiation sensor (FORS), which is composed of an inorganic scintillator, a plastic optical fiber (POF), a photomultiplier tube (PMT), and a multichannel analyzer (MCA), was developed for gamma-ray energy spectroscopy. In this study, we selected a cerium-doped lutetium yttrium orthosilicate (LYSO:Ce) as the sensitive element of the FORS and found that LYSO:Ce with dimensions of 3 × 3 × 15mm³ gives the best performance in obtaining a gammaray energy spectrum. The FORS allows us to measure the energy spectra of Co-60, Na-22, and Cs-137.     

Large enhancement of the thermoelectric Seebeck coefficient for amorphous oxide semiconductor superlattices with extremely thin conductive layers

Herein we demonstrate that amorphous oxide semiconductor (AOS) superlattices composed of a‐In–Zn–O (well) and a‐In–Ga–Zn–O (barrier) layers, fabricated on SiO₂ glass substrate by pulsed laser deposition at room temperature, exhibited an enhanced Seebeck coefficient |S |. The |S | value increases drastically with decreasing a‐In–Zn–O thickness (d_IZO) when d_IZO < ∼5 nm, and reached 73 µV K^–1 (d_IZO = 0.3 nm), which is ∼4 times larger than that of bulk |S |_3D (19 µV K^–1), while it kept its high electrical conductivity, clearly demonstrating that the quantum size effect can be utilized in AOS superlattices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Angular dependent photon-stimulated desorption of ions from a V2O5(010) surface

Using a display-type analyzer, we have measured the angular and energy distribution of O⁺ ions desorbed from a V₂O₅(010) surface by incident photons. The desorbed ions were mass-analyzed using time-of-flight gating techniques. The angular distribution of desorbed ions was found to be strongly peaked in the direction of the surface normal. This strongly directional desorption pattern reflects the local bonding geometry of the topmost oxygen atoms in the surface. The observed photoexcitation spectrum of the ion yiel can be explained with the core level Auger decay model formulated by Knotek and Feibelman.     

Nonself-similar regimes of isothermal collapse of protostellar clouds

We consider the development of inhomogeneity in the isothermal collapse of protostellar clouds. The initial and boundary conditions correspond to the classical statement of the problem on the contraction of a homogeneous cloud from a given volume. A centered rarefaction wave is shown to propagate from the outer boundary of the cloud toward its center at the first collapse stage. Analysis reveals two possible regimes of isothermal collapse, depending on the relationship between the rarefaction wave focusing time t^* and the cloud free-fall collapse time t_ff. For cold clouds, t^*=t _ff and the rarefaction wave is not reflected. In this case, as time elapses, the cloud collapse becomes self-similar with the characteristic density profile ρ～r^?2. In hot clouds, t*<t _ff and the focusing can take place before the formation of an opaque core. Since the velocities of the rarefaction wave along and across magnetic field lines in a magnetized cloud are different, its front assumes a shape elongated along magnetic field lines. Depending on the initial conditions, based on analytical estimates, we investigate various possible scenarios for the collapse of magnetic protostellar clouds.     

Second harmonic generation polarization microscopy with tightly focused linearly and radially polarized beams

Second harmonic generation microscopy was conducted on rat-tail tendons with linearly and radially polarized beams. Transverse and axial field components were generated in the focal region through tight focusing of linearly and radially polarized. It was found that the generated SHG signals could not be qualitatively explained with a scalar approximation to the electric field at the focus. Only by accounting for the interactions of the axial and transverse components of the electric field interacting through the nonlinear susceptibility χ⁽²⁾ tensor could the SHG images be explained. For the case of collagen we find that the SHG signal varies as a function of the analyzer angle with a cos² or sin² dependency for linearly polarized beams. For tightly focused radially polarized beams we find that the output SHG is radially polarized after collimation and is independent of the analyzer angle.     

Spin-dipole excitations of6Li in charged pion photoproduction

In the framework of bound shell model we have calculated the photoproduction of charged pions on⁶Li when spin-isospin dipole resonance is excited. It is shown that the transition strength concentrates in several energy regions. Such a gross-structure of the excitation spectrum is governed by the configurational splitting of the resonance. The excitation spectrum in⁶Li(γ, τ)-reaction is compared with the⁶Li(τ, γ), (e, e′) and (n, p)-reaction spectra where spin-isospin transitions are dominating too.     

The measurement of energy spectra of neutral particles in low energy ion scattering

An apparatus is described for low energy (0.1–10 keV) ion scattering (LEIS) experiments. A time of flight (TOF) spectrometer is incorporated in the system to be able to measure the energy of particles in the neutral state after scattering. The energy resolution ΔE/E of the TOF spectrometer is discussed and found to be 0.5% (FWHM). This is sufficient for our scattering experiments. An electrostatic analyzer (ESA) is used to measure the energy of scattered ions [ΔE/E=0.5% (FWHM)]. Experiments show that in general the ion dose needed to obtain a TOF spectrum (2×10¹⁰ ions/cm²) is much smaller than the dose needed for an ESA-spectrum (6×10¹³ ions/cm²). The ion spectra measured with the TOF spectrometer, by subtracting the neutral yield from the total yield, as well as with the ESA are found to agree quite well. This provides a way to calibrate the TOF spectrometer. The determination of the ion fraction of scattered particles is discussed [10 keV⁴⁰Ar⁺ on Cu(100), scattering angle 30°]. It is shown that the TOF spectrometer is able to measure light recoil particles (e.g. hydrogen) from a heavy substrate. In the analysing system is, in addition to the TOF spectrometer, also incorporated a stripping cell to measure the energy of neutral scattered particles. An energy spectrum of neutral scattered particles measured with both methods is shown.     

Galaxy formation just after the recombination period

A scenario of galaxy formation is outlined which is based essentially on the fact that the cosmic matter about 10⁶yr after the end of the recombination period is a general relativistic Boltzmann gas very close to equilibrium. In this scenario the observed very small inhomogeneities of the background radiation lead to very sharply edged gas clouds in the centres of the inhomogeneities. The universe between the clouds is completely swept clean of matter. If one assumes the centres of the inhomogeneities to be axially symmetric, the mass spectrum of the clouds extends from the smallest globular clusters withM 10⁵ M as the lower limit (spherical symmetry) up to the big spiral galaxies withM 10¹¹ M as the upper limit (maximal flattening). The upper limit masses are extremely thin pancakes which contract within a time interval of about 2 · 10⁹ years to the proportions of an ordinary spiral galaxy of today.     

激光诱导NO2分子500—532nm区荧光激发谱的实验研究

用准分子激光抽运可调谐染料窄带激光测定了室温下NO₂分子500—532nm区高分辨荧光激发谱,在两个较强吸收区505—510nm和513—520nm范围内标识了25个振动带,并作了转动分析,得到了相应的带头位置、转动常数和旋-转偶合常数等分子光谱常数,在25个振动带中有5个谱带是新发现的,所有得到转动分析的谱线均属于平行跃迁X～ ² A₁—A～²Ｂ₂,对实验结果的分析表明电子激发态A～ 关键词： 激光诱导荧光激发谱 振动带 转动分析