Observation of a saturation dip in the fluorescence light from electrodynamically trapped Ba+ ions

Ba⁺ ions are trapped in a Paul rf quadrupole trap and irradiated by D1 resonance light at 493.4 nm from a tunable laser. At ion densities of about 10⁵ cm^-3 a saturation lamp dip was easily observed when two laser beams of opposite directions were used. This should allow Doppler-free optical spectroscopy on a small number of ions in the future.     

Trapped ion density distribution in the presence of He-buffer gas

The spatial density distribution of Ba⁺ ions, confined in a rf quadrupole trap, has been measured by laser scanning across the trap. This allows to determine the ion temperature, assuming thermal equilibrium. Under UHV conditions the average ion energy has been found to be one tenth of the trap potential well depth. Collisions with He at pressures up to 5×10⁻⁶ mbar reduce the ion temperature by a factor of 3.     

Laser ablation loading of a radiofrequency ion trap

The production of ions via laser ablation for the loading of radiofrequency (RF) ion traps is investigated using a nitrogen laser with a maximum pulse energy of 0.17?mJ and a peak intensity of about 250?MW/cm². A?time-of-flight mass spectrometer is used to measure the ion yield and the distribution of the charge states. Singly charged ions of elements that are presently considered for the use in optical clocks or quantum logic applications could be produced from metallic samples at a rate of the order of magnitude 10⁵ ions per pulse. A linear Paul trap was loaded with Th⁺ ions produced by laser ablation. An overall ion production and trapping efficiency of 10^?7 to 10^?6 was attained. For ions injected individually, a dependence of the capture probability on the phase of the RF field has been predicted. In the experiment this was not observed, presumably because of collective effects within the ablation plume.     

Diode laser spectrometer at 493 nm for single trapped Ba+ ions

+ ions. Frequency doubling of a 100 mW diode laser at 986 nm results in up to 60 mW output power at 493 nm in a bandwidth of less than 60 kHz with respect to the cavity used for locking. Reference frequencies of 18 spectral lines of Te₂ near the 493 nm resonance of Ba⁺ have been measured using modulation transfer spectroscopy. The fluorescence excitation spectrum of a single Ba⁺ ion, measured with this laser, exhibits well-resolved dark resonances, which confirms the versatility of the system for quantum optical experiments. Received: 12 June 1998     

Precise - and -factor measurements of Ba+ isotopes

Laser-microwave double and triple resonance experiments were performed on clouds of Ba⁺ ions confined in a Penning ion trap to induce and detect electronic and nuclear spin flip transitions. Collisions with buffer gas molecules in the trap was used to reduce the lifetime of a long lived metastable state of the ions, in which population trapping might occur, and to cool the ions to the ambient temperature. Loss of ions from the trap by collisions were prevented by coupling the magnetron and reduced cyclotron motions by an additional r.f. field at the sum frequency of the two motions. Electronic Zeeman transitions in ¹³⁸Ba⁺ and ¹³⁵Ba⁺ were observed at a full width of about 3 kHz at a transition frequency of 80 GHz. The uncertainty of the line center was . From the magnetic field calibration by the cyclotron resonance of electrons stored in the same trap the g_J-factor for both isotopes could be determined to . From radiofrequency induced transitions of ¹³⁵Ba⁺ the nuclear g-factor could be determined . Both measurements improve earlier results by about one order of magnitude. Received: 9 July 1998 / Accepted: 14 July 1998     

Ion bunch stacking in a Penning trap after purification in an electrostatic mirror trap

The success of many measurements in analytical mass spectrometry as well as in precision mass determinations for atomic and nuclear physics is handicapped when the ion sources deliver “contaminations”, i.e., unwanted ions of masses similar to those of the ions of interest. In particular, in ion-trapping devices, large amounts of contaminant ions result in significant systematic errors—if the measurements are possible at all. We present a solution for such cases: The ions from a quasi-continuous source are bunched in a linear radio-frequency-quadrupole ion trap, separated by a multi-reflection time-of-flight section followed by a Bradbury–Nielsen gate, and then captured in a Penning trap. Buffer-gas cooling is used to damp the ion motion in the latter, which allows a repeated opening of the Penning trap for a stacking of mass-selected ion bunches. Proof-of-principle demonstrations have been performed with the ISOLTRAP setup at ISOLDE/CERN, both with ¹³³Cs⁺ ions from an off-line ion source and by application to an on-line beam of ¹⁷⁹Lu⁺ ions contaminated with ¹⁶³Dy¹⁶O⁺ ions. In addition, an optimization of the experimental procedure is given, in particular for the number of ion bunches captured as a function of the ions’ lifetimes and the parameters of the experiment .     

Spectral studies of Nd3+ and Er3+ ions in POCl3:SnCl4 laser liquid

The optical absorption spectra of triply ionized neodymium and erbium ions in POCl₃SnCl₄ laser liquid have been studied for the first time in the UV-VIS and NIR regions. Spectroscopic and Judd-Ofelt intensity parameters are evaluated from the observed band positions and their intensities. Radiative lifetimes and the luminescent branching ratios for the excited fluorescent levels of Nd³⁺ and Er³⁺ ions are theoretically estimated and the possible laser transitions are indicated. From the observed splittings of certain bands in the second-derivative spectrum of the Nd³⁺ ion, the crystal field (A ₂₀,A ₄₀) parameters are evaluated assumingC _3h symmetry for the ion.     

Ions and atoms in superfluid helium (4He)

New experimental results for mobilities in superfluid helium of the alkali earth ions Be⁺, Mg⁺, Ca⁺, Sr⁺ and Ba⁺ in the temperature region from 1.27 up to 1.66 K are reported. Surprisingly, the temperature dependence of the Be⁺ ion mobility, measured here for the first time, is more similar to that of the He⁺ ion than to the heavier alkali earth ions. This behavior may suggest a snowball like structure for the defect around Be⁺ in contrast to the bubble like defects around the heavier alkali earth ions.     

Optimum ion implantation and annealing conditions for stimulating secondary negative ion emission

The type, energy, ion dose, and heating temperature required to ensure a stable minimum work function of a surface in one experimental cycle (at least 2–3 min) are determined. Secondary ion mass spectrograms are recorded using Cs⁺, Ba⁺, and Ar⁺ ions. Cu, Al, and Mo samples are studied. The optimum ion implantation conditions and the activation temperature that provide a stable minimum work function of the sample surfaces are found. The samples implanted by Ba⁺ ions withstand higher temperature and current loads than the samples implanted by Cs⁺ ions. However, the work function in the case of Cs⁺ ions decreases stronger (to 1.9 eV). It is shown that neutral sputtered particles do not leave the surface at eφ ≤ 1.85–1.90 eV.     

Development of multiple laser frequency control system for Ca<Superscript>+</Superscript> isotope ion cooling

We here developed and evaluated a laser frequency control system which synchronizes the laser frequency to the resonance of target Ca ⁺ isotope ion whose having more than 8 GHz of isotope shift based on the Fringe Offset Lock method for simple operation of ICPMS-ILECS (Inductively Coupled Plasma Mass Spectrometry - Ion trap Laser Cooling Spectroscopy) The system fulfilled the minimum requirements of four slave lasers stability for Doppler cooling of Ca ⁺ ions. A performance of the system was evaluated by cooling ⁴⁰Ca ⁺ ions with the stabilized slave lasers. All the stable even Ca ⁺ isotope ions were trapped and their fluorescence was observed by switching laser frequencies using the system. An odd calcium isotope ⁴³Ca ⁺cooling was also succeeded by the control system.     

On the sensitivity of ion traps for spectroscopic applications

Ba⁺ ions, created by surface ionization near one endcap of an rf quadrupole trap were slowed down by collisions with the background gas. At He pressures of 10^?6 mbar or more 2% of the primary ions could be trapped. The sensitivity of ion detection by fluorescence radiation allows spectroscopic experiments, starting from less than 10⁷ particles. The observation of the ground-state hyperfine splitting of¹³⁷Ba⁺ is given as an example.     

Trapping of ions from high energy sources into a radiofrequency ion trap

An attempt is described to confine ions, created externally and accelerated to some energy, in an rf quadrupole trap. 4 keV Ba⁺ ions were stopped on a Ni foil, placed in an aperture of one trap electrode. The Ba then was evaporated from the heated foil and ionized by electron impact. At background pressure of about 10^–5 mbar of various light buffer gases (He, H₂, N₂), the trap was filled once with 10⁵ ions, at a minimum primary ion number of 10¹⁰. The storage time was 10 min. From the data obtained the possibility of spectroseopic experiments on rare isotopes, created with accelerators or nuclear reactors, is discussed.     

First principles study of nuclear quadrupole interactions in the molecular solid BF3 and the nature of binding between the molecules

The LPCTrap facility is coupled to the low-energy beam line LIRAT of the SPIRAL source at GANIL (France). The facility comprises an RFQ trap for beam preparation and a transparent Paul trap for in-trap decay studies. The system has been tested for several ion species. The Paul trap has been fully characterized for ⁶Li⁺ and ²³Na⁺ ions. This characterization together with GEANT4 simulations of the in-trap decay setup (Paul trap and detection system) has permitted to predict the effect of the size of the ion cloud on the decay study of ⁶He⁺.     

离子与通道相互作用对NaK 通道通透特性影响的研究

以NaK 通道的三维精细结构为基础,从理论上阐述了NaK 通道对钠离子、钾离子、铷离子以及钙离子的通透机理,钡离子可以作为NaK 通道阻断剂的微观机理,我们的研究结果表明,通道与离子的相互作用是决定通道对不同离子选择性的基础, 反映通道与离子相互作用的位能曲线是通道对不同离子通透性的外在表现. 关键词： NaK 通道 密度泛函 布朗动力学 通透性     

Lifetime measurements of metastable states in CRYRING

Collinear ion beam laser spectroscopy has been utilized in the ion storage ring CRYRING in order to measure lifetimes of metastable states in singly charged ions. The laser light has been used for selective probing of the population decay of individual fine structure or hyperfine structure states. With the use of a mechanical shutter, time resolved studies could be performed with millisecond resolution. In another experiment, the cw laser light was used to optically pump stored ions from the ground state into a specific metastable state. With most of the stored ions in the metastable state, direct observation of the decay of the forbidden transition from the metastable state to the ground state could be observed passively. Measurements of metastable lifetimes in Ca⁺, Sr⁺, Xe⁺ and Eu⁺ will be discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Concentration quenched luminescence and energy transfer analysis of Nd3+ ion doped Ba-Al-metaphosphate laser glasses

This paper reports the dopant ion (Nd³⁺) concentration effects on its luminescence properties in a new glass system based on barium-alumino-metaphosphates. Amongst the studied concentrations range of 0.276–13.31×10²⁰ ions/cm³, the glass with 2.879×10²⁰ ions/cm³ (1 mol%) Nd³⁺ concentration shows intense NIR emission from ⁴F_3/2 excited state, followed by a decrease in emission intensity for further increase in Nd³⁺ ion concentration. The observed luminescence quenching is ascribed to Nd³⁺ self-quenching through the donor-donor migration assisted cross-relaxation mechanism. The microscopic energy transfer parameters for donor-acceptor energy transfer, C _DA, and donor-donor energy migration, C _DD, have been obtained from the theoretical fittings to experimental decay curves and the spectral overlap model respectively. The C _DD parameters (×10^?39 cm⁶/sec) are found to be about three orders greater than that of C _DA (×10^?42 cm⁶/sec) for Nd³⁺ self-quenching in this host, demonstrating that the excitation energy migration among donors is due to the hopping mechanism. The energy transfer micoparameters obtained in the present study are comparable to the values reported for commercially available laser glasses LHG-8 and Q-98.     

Self-activated Nd:Ba2NaNb5O12 optical super-lattices: Micro characterization and non-collinear laser light generation

Czochralsky grown Nd³⁺-ion doped barium sodium niobate (Ba₂NaNb₅O₁₂, “banana”) optical super-lattices have been characterized by a combination of chemical etching, optical microscopy, micro-Raman and micro-photoluminescence experiments. The presence of ferroelectric domains, induced during growth process, is accompanied by a periodic modulation of Nd³⁺-ion concentration as well as by a small lattice distortion. When Nd³⁺-ion laser action at ≈1.06 μm is achieved under 0.808 μm laser diode pumping, the singularities of refractive index caused by opposed ferroelectric domains lead to non-collinear intra-cavity propagation.     

Towards a nuclear charge radius determination for beryllium isotopes

We propose determination of isotope shifts for radioactive beryllium isotopes using laser cooled ions in a linear radio frequency (RF) trap. Based on these measurements, combined with precise mass shift calculations, it will be possible to extract model-independent nuclear charge radii of ^7,9,10Be and the one-neutron halo ¹¹Be with precision better than 3%. Radioactive beryllium isotopes produced at ISOLDE and ionized with a laser ion source will be cooled and bunched in the radio frequency quadrupole buncher of ISOLTRAP. Ion temperatures will be reduced to the mK range by sympathetic cooling with co-trapped laser cooled ions in a specially designed two-stage linear RF trap. Resonances will be detected via fluorescence and frequencies measured with a femtosecond frequency comb.     

UV laser induced desorption of CsI and RbI ion clusters

Experimental results of laser sputtering of cesium and rubidium iodide secondary ions are presented. A TOF mass spectrometer, operating in linear mode, continuous extraction for positive or negative ions, was used for the analysis of (CsI)_nCs⁺, (CsI)_nI⁻, (RbI)_nRb⁺ and (RbI)_nI⁻ ion emission as a function of the laser irradiance. Experimental data show that the cluster ion emission yields decrease exponentially with n, for all the laser irradiances applied. Theoretical analysis of the clusters structure was performed using density functional theory at the B3LYP/LACV3P level, for the positive and negative cluster series. A quasi-equilibrium evolution of the clusters is proposed to extract a parameter characteristic of the cluster recombination process: the effective temperature. The hypothesis of the atomic species’ recombination (during the expansion of a high density highly ionized cloud) leading to cluster formation is confirmed to some extent in a second set of experiments: the UV laser ablation of a mixed and non-mixed cesium iodide and potassium bromide targets. These experiments show that the emission yields contain contributions from both the recombination process and from the sample stoichiometry, even for high laser irradiances.     

Structure and thermodynamic properties of positive and negative cluster ions in saturated vapour over barium dichloride

Geometrical structure, vibration spectra, and enthalpies of dissociation have been investigated for the ions BaCl₃^?, Ba₂Cl₃⁺, Ba₃Cl₅⁺, and Ba₄Cl₇⁺ which were detected earlier in the saturated vapour over BaCl₂. Quantum chemical methods of density functional theory, the second and the fourth order Møller–Plesset perturbation theory have been applied. The effective core potential with cc-pVTZ basis set for barium atom and two full-electron basis sets including the diffuse and polarised basis functions for chlorine atom were used. The effect of the basis set size and the computation method on the results was analysed. According to the results, all the ions possess the compact shaped structure. The equilibrium geometrical structures were found as follows: the planar D_3h for BaCl₃^?, triple bridged bipyramidal D_3h for Ba₂Cl₃⁺, hexabridged D_3h for Ba₃Cl₅⁺, and septuple bridged C_2v for Ba₄Cl₇⁺. For positive ions, the different isomeric structures were considered, but no isomers for these ions have been found. The geometrical parameters and vibration frequencies were utilised for computing of thermodynamic functions of the ions, and then the thermodynamic functions were used for the treatment of the experimental mass spectrometric data. The enthalpies of formation Δ_fH°(0 K) of the ions were determined (in kJ/mol): ?994 ± 6 (BaCl₃^?), ?481 ± 10 (Ba₂Cl₃⁺), ?1276 ± 14 (Ba₃Cl₅⁺), ?2048 ± 35 (Ba₄Cl₇⁺).