Laser Spectroscopy Experiments Research Articles

Status of laser spectroscopy measurements of long-lived antiprotonic and pionic helium atoms at CERN and PSI

The results of laser spectroscopy experiments of antiprotonic helium atoms carried out at the Antiproton Decelerator of CERN, and pionic helium atoms measured at the 590[Formula: see text]MeV ring cyclotron facility of the Paul Scherrer Institute are reviewed. The former experiment determined the antiproton-to-electron mass ratio as [Formula: see text]. In the latter, a resonant transition [Formula: see text] of pionic helium at a frequency of [Formula: see text][Formula: see text]GHz was detected. Some future perspectives are briefly described.

Laser spectroscopy of highly charged ions at the storage ring CSRe: Schottky-based spectroscopic investigation and XUV fluorescence detector development

Laser spectroscopy stands out as a powerful tool to investigate atomic and nuclear properties and also test fundamental theories by precisely measuring the energy levels in highly charged ions. In this work, the fine-structure splitting 1s22s2S1/2−1s22p2P1/2 transition in lithium-like 16O5+ has been investigated in a laser spectroscopy experiment at the heavy-ion storage ring CSRe. The excitation resonance of the tunable narrowband UV laser and the ions was observed using a Schottky resonator with very high sensitivity. The experimental uncertainties including the ion beam velocity determination, the space charge effects, laser wavelength calibration, and angular misalignment between the laser and ion beam were analyzed, and the 2S1/2−2P1/2 transition wavelength was determined to be λ0= 103.45(38) nm. The primary source of experimental uncertainty arises from the inaccurate measurement of the high voltage applied on the electron cooler and therewith the ion beam velocity at the CSRe. In order to solve this problem, a high-precision divider to precisely measure the high-voltage of the electron cooler is under construction, which is expected to improve the present experimental accuracy by three orders of magnitude. In addition, an XUV optical detector equipped with an off-axis parabolic mirror has been developed and installed at the CSRe for the investigation of slow dipole-forbidden transitions in highly charged ions, such as hyperfine splitting and M1 transitions. The experimental studies presented here pave the way for future laser spectroscopy experiments at the CSRe as well as at the future larger-scale scientific facility HIAF in China.

SATLAS2: An update to the package for analysis of counting data

SATLAS2 is a Python library that enables the user to fit counting data from laser spectroscopy experiments, in particular those that measure atomic hyperfine structures. In this analysis, the user can choose how the uncertainties are treated and can also opt to generate a random walk in order to present a fuller picture of the parameter space. The major upgrade compared to the previous version of SATLAS [1] is the different architecture of the codebase, which enabled a performance boost, with speed-up factors ranging from 20 to 300 times for various use cases. For backward compatibility, a translation layer between the two architectures is available, implementing only the core functionality of SATLAS. New version program summaryProgram Title: SATLAS2CPC Library link to program files:https://doi.org/10.17632/3hr8f5nkhb.2Developer's repository link:https://github.com/IKS-nm/satlas2Licensing provisions: MITProgramming language: PythonJournal reference of previous version: Computer Physics Communications, Volume 222, 2018, Pages 286-294, ISSN 0010-4655, https://doi.org/10.1016/j.cpc.2017.09.012Does the new version supersede the previous version?: YesReasons for the new version: Improved and more stable performanceSummary of revisions: The architecture of the SATLAS package has been completely changed. Instead of operating on Models, using SumModel and LinkedModel for various analysis options, SATLAS2 works with a central Fitter object to which Sources get assigned, which themselves get assigned Models. This structure improves the performance by streamlining the code and benefits from using a pass by reference approach for changing the parameters, rather than a pass by value. Most of the functionality is maintained, with a small interface for most basic things available so SATLAS2 can be used as a drop-in replacement.Nature of problem: The analysis of specifically counting data has some special considerations compared to more common datasets with Gaussian-distributed uncertainties. Application of Bayesian inference through random walk exploration is useful for more accurate exploration of parameter space. The fitting of multiple models with shared parameters can be desirable for either fitting multiple datasets with the same parameters or imposing additional restrictions on the parameters.Solution method: SATLAS2 implements the correct statistical costs for fitting of both counting data and Gaussian distributed uncertainties, and allows an easy implementation of custom cost functions.. Through the implementation of multiple Sources and Models, a natural extension of the fitting is made, so multiple models can be both summed together to fit to the same data and multiple fits can be linked together through parameter linking, using the underlying LMFIT [2] library. The ability to fit simultaneously increases the possibilities for extensive statistical analyses, and the interface through LMFIT with the emcee [3] library enables Bayesian exploration of the parameter space.

Collisional quenching of the pionic helium 4He long-lived states

Collisions of metastable pionic helium atoms with helium atoms of the medium lead to the destruction of these states, as well as to the shifts and broadening of E1 spectral lines of transitions between the pionic helium states. In the paper, in order to obtain the interaction potential matrix (π −He+)−He, calculations of the potential energy surface (PES) in the unrestricted Hartree-Fock method are performed taking into account electron correlations within the second-order perturbation theory (MP2). With this potential, the system of equations of strong channel coupling is solved numerically. Various techniques are used in the calculations that eliminate degeneracy of the solution matrix in the vicinity of small distances between colliding subsystems, which arises due to strong coupling of channels in this region, owing to which the numerical solutions “forget” boundary conditions. Cross sections and rates of collisional transitions are calculated (Nσv). It is found that the collisional transition rate (n, l) = (17, 16) → (17, 15) (n, l — the principal quantum number and the angular momentum respectively) for the density of the medium N = 0.2 × 1023 cm−3 is lower than 103s−1, which indicates that it is possible to ignore the effect of collisional destruction of pionic helium long-lived states in precision laser spectroscopic experiments.

Control and data acquisition system for collinear laser spectroscopy experiments

Control and data acquisition system for collinear laser spectroscopy experiments

Laser spectroscopic studies of long-lived pionic helium at PSI

A recent laser spectroscopy experiment of three-body pionic helium atoms which was carried out using the 590 MeV ring cyclotron facility of the Paul Scherrer Institute (PSI) is briefly reviewed. The charged pion mass may be precisely determined by measuring the transition frequency of the pionic atom and comparing the results with quantum electrodynamics (QED) calculations. The experimental methods used to detect the atomic resonance are described.

Large nuclear scattering effects in antiproton transmission through polymer and metal-coated foils

We simulate the deceleration and transmission of antiprotons with keV-scale kinetic energies through polymer foils using a molecular dynamics approach, which includes a model of nuclear stopping based on the attractive interaction potentials between antiprotons and target atoms calculated by quantum chemical methods. Antiprotons scatter into larger angles with higher cross sections than protons. This causes a significant fraction of antiprotons to annihilate in the foil instead of emerging with energies of a few keV, especially when coatings of materials with high atomic number are applied to the surfaces. The simulation results are in good agreement with data from two experiments that involved pulsed antiproton beams with incident energies between 63 keV and 122 keV that traverse polymer foils with thicknesses of $\ensuremath{\approx}1.3$ $\ensuremath{\mu}\mathrm{m}$ and 1.8 $\ensuremath{\mu}\mathrm{m}$. The 25-nm-thick layers of Ag on the latter foil reduced the transmission of antiprotons. The results will be utilized to design the degrader foils in laser spectroscopy experiments of antiprotonic helium atoms and experiments involving Penning traps that are carried out at the ELENA facility of CERN.

Recent progress of laser spectroscopy measurements of pionic helium

We review the results of recent laser spectroscopy experiments on metastable pionic helium atoms at the Paul Scherrer Institute’s 590 MeV cyclotron facility that was carried out by the PiHe collaboration. Some future perspectives are briefly discussed.

A Review of Novel Instrumentation for Matrix Independent Ultratrace Analysis of Radionuclides using Collinear Resonance Ionisation Spectroscopy (CRIS)

The CRIS setup at CERN-ISOLDE is a high resolution laser spectroscopy experiment that is used to characterise exotic radionuclei with very low production rates. Acquisition of hyperfine spectra enable nuclear spins and precise values of nuclear magnetic dipole and electric quadrupole moments to be determined. The high sensitivity of the CRIS technique combined with the high selectivity make it an ideal candidate for quantitation of analytes in complex matrices. This review article reports on novel instrumentation under development at the University of Manchester, utilising the CRIS technique for targeted matrix independent ultra-trace analysis.

Second Harmonic Generation in Germanium Quantum Wells for Nonlinear Silicon Photonics

Second-harmonic generation (SHG) is a direct measure of the strength of second-order nonlinear optical effects, which also include frequency mixing and parametric oscillations. Natural and artificial materials with broken center-of-inversion symmetry in their unit cell display high SHG efficiency, however, the silicon-foundry compatible group IV semiconductors (Si, Ge) are centrosymmetric, thereby preventing full integration of second-order nonlinearity in silicon photonics platforms. Here we demonstrate strong SHG in Ge-rich quantum wells grown on Si wafers. Unlike Si-rich epilayers, Ge-rich epilayers allow for waveguiding on a Si substrate. The symmetry breaking is artificially realized with a pair of asymmetric coupled quantum wells (ACQW), in which three of the quantum-confined states are equidistant in energy, resulting in a double resonance for SHG. Laser spectroscopy experiments demonstrate a giant second-order nonlinearity at mid-infrared pump wavelengths between 9 and 12 μm. Leveraging on the strong intersubband dipoles, the nonlinear susceptibility χ(2) almost reaches 105 pm/V, 4 orders of magnitude larger than bulk nonlinear materials for which, by the Miller’s rule, the range of 10 pm/V is the norm.

Hypersonic nozzle for laser-spectroscopy studies at 17 K characterized by resonance-ionization-spectroscopy-based flow mapping

The in-gas-jet laser spectroscopy method relies on the production of uniform and low-temperature gas jets to fully resolve the atomic hyperfine structure and efficiently determine fundamental nuclear properties of short-lived isotopes from, e.g., the hardly accessible actinide and transactinide elements. In this article we present the studies devoted to designing, producing, and characterizing the flow properties of a convergent-divergent (de Laval) hypersonic nozzle with a superior performance for laser spectroscopy applications. A novel flow mapping technique, based on resonance ionization spectroscopy (RIS), has been employed to characterize the local flow properties of an argon gas jet formed by this nozzle, revealing a 61.5-mm long, highly collimated atomic jet at a uniform low temperature of 16.6(5) K [Mach 8.11(12)] that will enable laser spectroscopy experiments on heavy-exotic nuclei with an unprecedented spectral resolution and a high efficiency. These results have been compared with those obtained by planar laser induced fluorescence spectroscopy (PLIFS) studies and show a good agreement between the two techniques and a significant improvement in efficiency of the RIS mapping method with respect to PLIFS. The data are compared to state-of-the-art fluid-dynamics calculations that were carried out to obtain the nozzle contour and simulate its performance, as well as to explain the observation of a possible onset of argon nucleation.

A Miniature Permanent Magnet Assembly with Localized and Uniform Field with an Application to Optical Pumping of Helium

Atomic state preparation can benefit from a compact and uniform magnetic field source. Simulations and experimental measurements have been used to design, build, and test such a source and then apply it to the optical pumping of atomic helium. This source is a 9.5 mm (3/8″) OD × 6.7 mm (1/4″) ID × 9.5 mm (3/8″) long, NdFeB-N42 assembly of 1.6 mm (1/16″) thick customized annular magnets. It has octupole decay with a residual dipole far field from imperfect dipole cancelations. Fast B-field decay localizes the field, minimizing the need for shielding in applications. It has a greater than 50% clear aperture with a uniform and collimated magnetic field consistent with the prediction of several models. The device is applied to a high precision 3,4He laser spectroscopy experiment using σ+ or σ− optical pumping currently resulting in a measured 99.3% preparation efficiency and in accordance with a rate equation model.

Recent results of laser spectroscopy experiments of pionic helium atoms at PSI

A review of a recent experiment carried out at PSI involving laser spectroscopy of metastable pionic helium (\pi{^4He}^+\equiv\pi^{-}+{^4He}^{2+}+e^-π4He+≡π−+4He2++e−) atoms is presented. An infrared transition (n,\ell)=(17,16)(n,ℓ)=(17,16)\rightarrow→(17,15)(17,15) at a resonance frequency of \nu\approx 183760ν≈183760 GHz was detected.

Laser frequency stabilization via bichromatic Doppler-free spectroscopy of an 87Rb D1 line.

We demonstrate a bichromatic Doppler-free spectroscopy of an 87RbD1 line by using a dual-frequency, counterpropagating laser field with orthogonal linear polarizations. A reversed Doppler-free resonance dip is observed in the dual-frequency scheme, and a significant improvement of frequency discrimination curve is acquired due to the coherent population trapping (CPT) effect. The influence of the static magnetic field and laser intensity on the spectroscopy is studied in both single- and dual-frequency schemes. After locking the laser frequency to the 87RbD1 line in the dual-frequency stabilization scheme, the beat note fractional frequency stability is at the level of 7×10-12 at 1 s integration time. This technique can be used in various applications, such as CPT atomic clocks, laser spectroscopy, quantum optics, and laser-cooling experiments.

Compilation of recent nuclear ground state charge radius measurements and tests for models

The root-mean-square (rms) charge radii of 236 nuclides measured by laser spectroscopy experiment are compiled, and the uncertainties are calculated. From the rms charge radii of Mg isotope chain, the new magic number N=14 can be observed, and the traditional magic number N=20 disappears in the K isotope chain. A good linear relationship between the difference of the mirror nuclear charge radii and the isospin asymmetry can be clearly observed with a Pearson’s linear correlation coefficient of 0.96. The accuracies and predictive powers of the WS* and HFB25 models are tested with these new data. The rms deviation with the WS* model is only 0.0176 fm for the 129 new data, which is much better than that of HFB25 model. The influence of deformation effect on nuclear charge radius prediction is studied systematically.

Laser spectroscopy of the ^2{mathrm{S}}_{1/2}{-}^2{mathrm{P}}_{{1}/2}, ^2{mathrm{P}}_{3/2} transitions in stored and cooled relativistic C3+ ions

The ^2{mathrm{S}}_{1/2}{-}^2{mathrm{P}}_{{1}/2} and ^2{mathrm{S}}_{1/2}{-}^2{mathrm{P}}_{{3}/2} transitions in Li-like carbon ions stored and cooled at a velocity of beta approx 0.47 in the experimental storage ring (ESR) at the GSI Helmholtz Centre in Darmstadt have been investigated in a laser spectroscopy experiment. Resonance wavelengths were obtained using a new continuous-wave UV laser system and a novel extreme UV (XUV) detection system to detect forward emitted fluorescence photons. The results obtained for the two transitions are compared to existing experimental and theoretical data. A discrepancy found in an earlier laser spectroscopy measurement at the ESR with results from plasma spectroscopy and interferometry has been resolved and agreement between experiment and theory is confirmed.

Dynamics of coordination of H3O+ and NH4+ in crown ether cavities.

Crown ethers stand out for their ability to form inclusion complexes with metal cations and positively charged molecular moieties. Hydronium and ammonium interact strongly with crown ethers and potentially modulate their ionophoric activity in protic solvents and physiological environments commonly involved in (bio)technological applications. In this work, Born-Oppenheimer molecular dynamics (BOMD) computations are employed to gain insights into the coordination arrangements of H3O+ and NH4+ in the complexes with the native crown ethers 15-crown-5 (15c5) and 18-crown-6 (18c6). Both cations display dynamic changes in coordination inside the cavities of the crown ethers. On the one hand, hydronium explores different coordination arrangements, through rotation around its C3 axis in the 15c5 complex, and through breathing motions, involving rapid inversions of the O atom along the C3 axis in the 18c6 complex. On the other hand, ammonium undergoes a facile rotation in three dimensional space, leading to frequent changes in the NH bonds involved in the coordination with the crown ether. The reduced host-guest symmetry matching of the 15c5 macrocycle enhances the reorientation dynamics and, in the case of H3O+, it promotes short H-bonding distances yielding events of proton transfer to the crown ether. The infrared vibrational spectra predicted by the BOMD computations within this dynamic framework reproduce with remarkable accuracy the action spectra of the isolated complexes obtained in previous infrared laser spectroscopy experiments. The experimentally observed band positions and broadening can then be rationalized in terms of orientational diffusion of the cations, changes in the coordinating H-bonding pairs sustaining the complex and eventual proton bridge formation.

Gas cell studies of thorium using filament dispensers at IGISOL

Filament-based dispensers of thorium have been investigated at the IGISOL facility, Jyväskylä, for potential use as a thorium ion source for future collinear laser spectroscopy experiments. Several different filaments were manufactured in the Institute of Atomic and Subatomic Physics of TU Wien, with 232Th and 229Th prepared on tantalum substrates either by drying thorium nitrate solution or via molecular plating, while adding a layer of zirconium for oxide reduction. The filaments were characterized in a helium-filled gas cell by performing selective and efficient in-gas-cell resonance laser ionization and by analyzing the resulting ion beams by mass spectrometry. Additionally, the in-gas-cell laser ionization process of thorium was further characterized by wavelength scans, saturation measurements and by recording the temporal behavior of extracted ion pulses. Although an ion source was successfully created with mass-separated intensities over 106 ions/s, the required high filament temperature resulted in significant contributions from interfering impurities and deterioration of the filament structure.

Exotic Nuclear Structure of Neutron-rich Zn Isotopes

Nuclear structure of unstable nuclei, in particularly the nuclei near the magic number, has been one of the hot topics of nuclear physics study. Near the neutron magic number N=40, 50, rich nuclear structure phonomania appeared in the nickel region, in particularly for the neutron-rich isotopes, have stimulated intensive investigation from both theoretical and experimental aspects. In order to gain a better understanding of the nuclear structure in the nickel region, we choose to study the properties of neutron-rich Zn(Z=30) isotopes. In this paper, after a simple introduction of the laser spectroscopy experiment of Zn isotopes at CERN-ISOLDE, we reviewed the nuclear spins, magnetic moment, electric quadrupole moment and root mean square charge radius of the ground and long-lived isomeric states of 62–80Zn isotopes. Based on these properties, together with shell-model calculation from different interactions, we discussed systematically the nuclear structure phenomena, such as the shell structure evolution, magicity, deformation and shape coexistence, and the cross-shell excitation of correlated nucleons. At the end, on the basis of the current experimental data and nuclear structure information, as well as the theoretical prediction of energy level evolution of N=51 isotones in nickel region, we propose to measure the basic properties of 81,82Zn nuclei at the collinear resonance ionization spectroscopy setup at ISOLDE-CERN.

On the performance of wavelength meters: Part 1—consequences for medium-to-high-resolution laser spectroscopy

Present-day laser-spectroscopy experiments increasingly rely on modern commercial devices to monitor, stabilize, and scan the wavelength of their probe laser. Recently, new techniques are capable of achieving unprecedented levels of precision on atomic and nuclear observables, pushing these devices to their performance limits. Considering the fact that these observables themselves are deduced from the frequency difference between specific atomic resonances, in the order of MHz–GHz, the uncertainty on the output of the device measuring the wavelength is often directly related to the final systematic uncertainty on the experimental results. Owing to its importance, the performance of several commercial wavelength meters was compared against different reference sources, including a Scanning Fabry–Perot Interferometer (SFPI) and a frequency comb. Reproducible, wavelength- and device-dependent disagreements are observed, potentially skewing the experimental output at high precision. In this paper, a practical and relatively inexpensive wavelength meter characterization procedure is presented and validated. This method is capable of improving the precision on wavelength differences considerably depending on the device, while together with a second investigation that is published separately, (Konig et al., in Appl Phys B, 2020), it offers a full description of the expected wavelength meter performance for users.