Laser cooling of Cd<Superscript>+</Superscript> ions using a microwave transition as a repumping process

Cadmium ions trapped in a linear Paul trap have been laser cooled by use of a microwave transition as a repumping process. A 15.2-GHz microwave transition between a ground-state hyperfine splitting is used for repumping, while an all-solid-state laser with the wavelength of 214 nm drives the cooling transition between the ² S _1/2 and ² P _3/2 states. A phase transition from the cloud state to the crystal state of trapped ions has been observed both in fluorescence spectra and in images of an ion string. Cadmium ions have potential of application for quantum information processing where the ground-state microwave transition is used for both a repumping process and manipulation of quantum states of trapped ions. PACS 32.80.Pj     

A single laser system for ground-state cooling of <Superscript>25</Superscript>Mg<Superscript>+</Superscript>

We present a single solid-state laser system to cool, coherently manipulate and detect ²⁵Mg⁺ ions. Coherent manipulation is accomplished by coupling two hyperfine ground state levels using a pair of far-detuned Raman laser beams. Resonant light for Doppler cooling and detection is derived from the same laser source by means of an electro-optic modulator, generating a sideband which is resonant with the atomic transition. We demonstrate ground-state cooling of one of the vibrational modes of the ion in the trap using resolved-sideband cooling. The cooling performance is studied and discussed by observing the temporal evolution of Raman-stimulated sideband transitions. The setup is a major simplification over existing state-of-the-art systems, typically involving up to three separate laser sources.     

Hyperfine magnetic anomaly in isotopic pairs <Superscript>151, 152</Superscript>Eu and <Superscript>152, 153</Superscript>Eu

High-resolution laser spectroscopy measurements of optical hyperfine splitting on the ^{151, 152, 153}Eu isotopes were performed on the atomic transition 4f ⁷6s ^{2 8} S _7/2 → 4f ⁷6s6p ⁶ P _5/2 at λ ≈ 564.58 nm. Values of the nuclear magnetic dipole and electric quadrupole moments are obtained from the measured hyperfine splitting and the magnetic hyperfine anomalies in the isotope pairs ^{151, 152}Eu and ^{152, 153}Eu are deduced. The absolute values of the hyperfine anomaly in both cases are unusually large: 5 (1)%. The possible sources causing these anomalies are discussed.     

Hyperfine structure and isotope shifts of neutron-rich138–146Cs

The 6s²S_1/2-7_p ²P_3/2 transition in^138–142Cs (λ=455.5 nm) has been investigated by high-resolution collinear laser spectroscopy in a fast atomic beam. The isotopes are obtained by on-line mass separation of fission products. Nuclear moments and changes of mean-square charge radii are derived from hyperfine structure and isotope shift.     

Nuclear radii of thorium isotopes from laser spectroscopy of stored ions

Isotope shifts and hyperfine splittings in optical transitions for atomic ions of the thorium isotopes²²⁷Th to²³⁰Th and²³²Th have been measured by laser spectroscopy on stored ions. From the isotope shift data, changes of the mean square charge radii are determined. A continuous increase of the charge radius with mass numberA is observed, in agreement with droplet model calculations. The results indicate that the odd-even staggering for Th is different from that one of the neighbouring isotones of Fr and Ra. There is some empirical evidence from systematics for an inversion of the staggering and the appearance of an octupole deformation atN ≦137. The hyperfine splitting for²²⁹Th for 3 electronic levels is given.     

Radio-frequency laser double-resonance spectroscopy of trapped171Yb ions and determination of line shifts of the ground-state hyperfine resonance

The paper reports on radio-frequency laser double-resonance experiments on¹⁷¹Yb ions confined in a cylindrically symmetric electrodynamic trap in the presence of helium buffer gas. The optical-excitation scheme relies on the selective excitation of a cycling hyperfine component of the = 370 nm resonance transition. Additional excitation of a transition at = 935 nm prevents population trapping of ions in the metastable² F _7/2 level. Using a maser reference, the ground-state hyperfine resonance frequency is measured under conditions of a systematic variation of confinement conditions. Kinetic temperatures and the resulting relativistic resonance shifts are inferred from the inhomogeneous broadening of the optical resonance transition. Shifts of the hyperfine resonance frequency due to quadratic Stark effect and collisions are determined. By extrapolation, the unperturbed transition frequency is determined as 12 642 812 118.471 (9) Hz.     

Wigner crystals of 229Th for optical excitation of the nuclear isomer

We have produced laser-cooled Wigner crystals of 229Th3+ in a linear Paul trap. The magnetic dipole (A) and electric quadrupole (B) hyperfine constants for four low-lying electronic levels and the relative isotope shifts with respect to 232Th3+ for three low-lying optical transitions are measured. Using the hyperfine B constants in conjunction with prior atomic structure calculations, a new value of the spectroscopic nuclear electric quadrupole moment Q=3.11(16) eb is deduced. These results are a step towards optical excitation of the low-lying isomer level in the 229Th nucleus.     

A high-stability semiconductor laser system for a <Superscript>88</Superscript>Sr-based optical lattice clock

We describe a frequency-stabilized diode laser at 698 nm used for high-resolution spectroscopy of the ¹S₀–³P₀ strontium clock transition. For the laser stabilization we use state-of-the-art symmetrically suspended optical cavities optimized for very low thermal noise at room temperature. Two-stage frequency stabilization to high-finesse optical cavities results in measured laser frequency noise about a factor of three above the cavity thermal noise between 2 Hz and 11 Hz. With this system, we demonstrate high-resolution remote spectroscopy on the ⁸⁸Sr clock transition by transferring the laser output over a phase noise-compensated 200-m-long fiber link between two separated laboratories. Our dedicated fiber link ensures a transfer of the optical carrier with frequency stability of 7×10⁻¹⁸ after 100 s integration time, which could enable the observation of the strontium clock transition with an atomic Q of 10¹⁴. Furthermore, with an eye toward the development of transportable optical clocks, we investigate how the complete laser system (laser+optics+cavity) can be influenced by environmental disturbances in terms of both short- and long-term frequency stability.     

Isotope shift and hyperfine structure measurements at the242f Am fission isomer

Istope shift and hyperfine structure measurements have been performed for the^242fAm fission isomer with target production rates of only a few per second. The method is based on resonance ionization spectroscopy (RIS) in a buffer gas cell with radioactive decay detection of the ionization process (RADRIS). A relative isotope shift ratioX _exp=IS^242f,241/ IS^243,241=41.7±0.9 has been measured for the 500.02 nm transition corresponding to a nuclear parameter ^242f,241=5.4±0.3 fm². The analysis of the quadrupole moment based on the deformed Fermi-model of the nuclear charge distribution including second order corrections results inQ ₂₀=38.2 ±1.4( _–0.8 ^+0.4 )_model eb. The measurement of the hyperfine structure splitting of the transition at 466.28 nm yields a negativeg-factor and a nuclear spin ofI=2 orI=3.Work supported by the Bundesministerium für Bildung und Forschung under contract 06 MZ 5661.     

On the hyperfine structures of the ground state(s) in the <Superscript>6</Superscript>Li and <Superscript>7</Superscript>Li atoms

The hyperfine structure of the ground 2²S-states of the three-electron atoms and ions is investigated. By using our recent numerical values for the doublet electron density at the atomic nucleus, we determine the hyperfine structure of the ground (doublet) 2²S-state(s) in the ⁶Li and ⁷Li atoms. Our predicted values (228.2058 and 803.5581 MHz, respectively) agree well with the experimental values 228.20528(8) MHz (⁶Li) and 803.50404(48) MHz (⁷Li [R.G. Schlecht and D.W. McColm, Phys. Rev. 142, 11 (1966)]). The hyperfine structures of a number of lithium isotopes with short lifetimes, including ⁸Li, ⁹Li, and ¹¹Li atoms are also predicted. The same method is used to obtain the hyperfine structures of the three-electron ⁷Be⁺ and ⁹Be⁺ ions in their ground 2²S-states. Finally, we conclude that our approach can be generalized to describe the hyperfine structure in the triplet n³S-states of the four-electron atoms and ions.     

Characterization of a dual-etalon Ti:sapphire laser via resonance ionization spectroscopy of stable copper isotopes

Resonance ionization spectroscopy (RIS) inside a buffer gas-filled ion guide is a very sensitive tool for a first determination of nuclear moments and charge radii of radioactive isotopes produced using the IGISOL technique. Currently employed pulsed Ti:sapphire laser systems have a typical laser linewidth of 5 GHz in the fundamental, which in many cases is the dominant line broadening effect. We present results of RIS on stable ^63,65Cu using a dual-etalon Ti:sapphire laser with a reduced linewidth of 1 GHz. Determination of hyperfine parameters of ⁶³Cu revealed discrepancies when compared to existing higher resolution data. A study of systematic uncertainties is underway using a homemade scanning Fabry-Pérot interferometer (FPI). A real-time recording of the mode structure of the multi-longitudinal mode Ti:sapphire laser during a scan of the 244.238 nm atomic ground state transition in parallel with the readout from the commercial wavemeter has identified sources of uncertainty.     

Inner-shell excited quartet states in Li-like O<Superscript>5+</Superscript> and Ne<Superscript>7+</Superscript> ions

First laser spectroscopic measurements of the 6s5d³D₁-6s6p¹P₁ and 6s5d³D₂-6s6p¹P₁ transitions in several isotopes of atomic barium have been performed. The hyperfine structure of these transitions was optically resolved and isotope shifts for even and odd isotopes were determined. The isotope shifts show a deviation from their expected behavior for odd isotopes in an analysis based on King-plots. This observation puts atomic structure calculations at test because available theories do not predict this. A profound understanding of the wavefunctions for heavy alkaline earth systems like barium (Ba) and radium (Ra) is essential for a theoretical evaluation of their sensitivity to fundamental symmetry breaking effects such as they could be observed, e.g., through permanent electric dipole moments. Further the absolute frequency of the 6s^{2 1}S₀-6s6p³P₁ intercombination line in ¹³⁸Ba was determined to be 12 636.6232(1) cm^-1.     

Blue laser cooling transitions in Tm I

We have studied possible candidates for laser cooling transitions in ¹⁶⁹Tm in the spectral region of 410–420 nm. By means of saturation absorption spectroscopy, we have measured the hyperfine structure and rates of two nearly closed cycling transitions from the ground state 4f¹³6s²(²F₀)(J_g=7/2) to upper states 4f¹²(³H₅)5d_3/26s²(J_e=9/2) at 410.6 nm and 4f¹²(³F₄)5d_5/26s²(J_e=9/2) at 420.4 nm and evaluated the life times of the excited levels as 15.9(8) ns and 48(6) ns, respectively. Decay rates from these levels to neighboring opposite-parity levels are evaluated by means of Hartree–Fock calculations. We conclude that the strong transition at 410.6 nm has an optical leak rate of less then 2×10^-5 and can be used for efficient laser cooling of ¹⁶⁹Tm from a thermal atomic beam. The hyperfine structure of two other even-parity levels, which can be excited from the ground state at 409.5 nm and 418.9 nm, is also measured by the same technique. In addition, we give a calculated value of 7(2) s^-1 for the rate of magnetic-dipole transition at 1.14 μm between the fine structure levels (J_g=7/2)↔(J’_g=5/2) of the ground state which can be considered as a candidate for applications in atomic clocks. PACS 32.70.Cs; 32.10.Fn; 32.80.Pj     

Hyperfine-structure studies of the 1s<Superscript>2</Superscript>2snp (n=2, 3) <Superscript>3</Superscript>P states for the beryllium isoelectronic sequence

The hyperfine structure parameters of the 1s²2snp (n=2, 3) ³P states for the beryllium isoelectronic sequence from Z= 4 to 10 are calculated with the full-core plus correlation (FCPC) wave functions. For the 1s²2s2p ³P state of the beryllium atom, the calculated fine structure parameters are in good agreement with the latest theoretical and experimental data in the literature. It is shown that hyperfine constants of the low-lying excited states for the beryllium atom can be calculated accurately using this theoretical method. For 1s²2snp (n=2, 3) ³P states of the beryllium isoelectronic sequence, our predictions may provide valuable reference data for other theoretical calculations and experimental measurements in future.     

The beta-decay scheme of <Superscript>232</Superscript>Fr and the K = 0 ground-state band in <Superscript>232</Superscript>Ra

The beta-decay of ²³²Fr to excited states in ²³²Ra has been studied using gamma-gamma coincidence detection combined with the isotope separator on-line technique at the ISOLDE PSB facility at CERN. Earlier findings are confirmed and three new gamma lines are reported. In addition to the beta-decay characteristics of ²³²Fr, the K = 0 ground-state band in ²³²Ra is identified. A yield survey of neutron-rich Fr isotopes, important also for the EURISOL project, is incorporated.Received: 20 April 2004, Revised: 12 May 2004, Published online: 13 July 2004PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 23.20.-g Electromagnetic transitions - 28.60. + s Isotope separation and enrichment - 29.25.Rm Sources of radioactive nuclei     

Nuclear moments and the change in the mean square charge radius of neutron deficient thallium isotopes

The hyperfine structure, isotope and isomeric shifts in the atomic transition 6p ² P _3/2–7s ² S _1/2, =535 nm have been measured for theI=7 andI=2 states of^{190, 192, 194, 196}Tl; theI=1/2 andI=9/2 states of¹⁹¹Tl and the I=7 isomer of¹⁸⁸Tl. The thallium isotopes were prepared as fast atomic beams at the GSI on-line mass separator following fusion reactions and — in some cases — subsequent-decay. The nuclear dipole moments, electric quadrupole moments and the change in the nuclear mean square charge radius are evaluated. Theuu-isotopes show an isomeric shift which changes sign between¹⁹²Tl and¹⁹⁴Tl.Dedicated to P. Armbruster on the occasion of his 60th birthday     

Sub-Doppler fluorescence on the atomic <Emphasis Type="Italic">D</Emphasis><Subscript>2</Subscript> line of a submicron rubidium-vapor layer

An extremely thin cell (ETC) with the thickness of a Rb atomic vapor layer in the range of 100–300 nm was fabricated. It is demonstrated that a simple laser-diode technique with a single resonant light beam is sufficient to observe separately all of the atomic hyperfine transitions of the D ₂ line of Rb (780 nm) and also allows us to measure the relative transition probabilities of the hyperfine transitions. The onset of collisional self-broadening of the hyperfine transitions as the number density of atoms increases was studied. The detrimental role of the atoms with slow longitudinal velocity in the sub-Doppler response of the Rb ETC is demonstrated by studies in which the cell is tilted from normal incidence of the laser beam. It is also shown that using an ETC allows us to resolve in a moderate external magnetic field the Zeeman splitting of the hyperfine transitions of the ⁸⁷Rb D ₁ transition F _g=1F _e=1,2. Received: 19 February 2003 / Revised version: 4 April 2003 / Published online: 2 June 2003 RID="*" ID="*"Corresponding author. Fax: +374/32-31172, E-mail: david@ipr.sci.am     

Diode-pumped Pr<Superscript>3+</Superscript>:YAlO<Subscript>3</Subscript>/LBO violet laser at 374 nm

We report a diode-pumped Pr³⁺:YAlO₃ laser emitting at 747 nm. A power of 232 mW at 747 nm has been achieved in continuous-wave operation with a diode emitting 2 W at 448 nm. Furthermore, intracavity second-harmonic generation in continuous-wave mode has also been demonstrated with a power of 52 mW at 374 nm by using a LBO nonlinear crystal. The fluctuation of the violet output power was better than 2.3%. The beam quality M ² value is 2.2.     

Investigation of Rb <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript> atomic lines in strong magnetic fields by fluorescence from a half-wave-thick cell

It has been experimentally demonstrated that the use of the effect of significant narrowing of the fluorescence spectrum from a nanocell that contains a column of atomic Rb vapor with a thickness of L = 0.5λ (where λ = 794 nm is the wavelength of laser radiation, whose frequency is resonant with the atomic transition of the D ₁ line of Rb) and the application of narrowband diode lasers allow the spectral separation and investigation of changes in probabilities of optical atomic transitions between levels of the hyperfine structure of the D ₁ line of ⁸⁷Rb and ⁸⁵Rb atoms in external magnetic fields of 10–2500 Gs (for example, for one of transitions, the probability increases ∼17 times). Small column thicknesses (∼390 nm) allow the application of permanent magnets, which facilitates significantly the creation of strong magnetic fields. Experimental results are in a good agreement with the theoretical values. The advantages of this method over other existing methods are noted. The results obtained show that a magnetometer with a local spatial resolution of ∼390 nm can be created based on a nanocell with the column thickness L = 0.5λ. This result is important for mapping strongly inhomogeneous magnetic fields.     

Growth defect W<Superscript>3+</Superscript>-W<Superscript>2+</Superscript> of CdWO<Subscript>4</Subscript> crystals

CdWO₄ crystals grown by the Czochralski method at the low-temperature gradient were investigated with electron spin resonance (ESR) spectroscopy. ESR spectra did not contain the spectra of impurity ions typical for the CdWO₄ structure, i.e., Fe³⁺, Mn²⁺, and Cr³⁺. At the same time, in the studied crystals a complex ESR spectrum having the hyperfine structure due to two nonequivalent tungsten atoms was observed (W¹⁸³;I=1/2; natural abundance, 14.28%). Angular dependence analysis and simulation of ESR spectra have shown that this novel spectrum is described by a spin-Hamiltonian with the following parameters:D=839 G,E=80 G,g _xx=2.01,g _yy=1.97,g _zz=1.987 and electron spinS=7/2. There is one magnetically nonequivalent position of the center in the crystal structure and the direction ofD _zz andg _zz corresponds to the direction of W_n-W_n+2 (or Cd_n-Cd_n+2) in the crystal structure. Because of the fact that it is in principle impossible to achieve the electron stateS=7/2 for the d-shell of one transition metal ion and taking into account the fact that such electron state is realized for two nonequivalent tungsten atoms, we suppose the defect structure to be the chain W²⁺-M⁺-W³⁺. In the structure of this defect the ion M⁺ is diamagnetic, the ions W²⁺ and W³⁺ have electron spinS=2 andS=3/2, respectively. The necessary condition for such defect to exist is to place this chain of ions in cadmium positions for the charge compensation. the reason for such defects to form is supposed to be the incorporation of M⁺ ions into the CdWO₄ lattice. The presence of W²⁺ and W³⁺ in Cd positions in the defect structure provides the charge compensation and the lowering of the lattice stress.