Measuring the difference in nuclear charge radius of Xe isotopes by EUV spectroscopy of highly charged Na-like ions

The difference in the mean-square nuclear charge radius of xenon isotopes was measured utilizing a method based on extreme ultraviolet spectroscopy of highly charged Na-like ions. The isotope shift of the Na-like D1 (3s 2 S 1/2 - 3p 2 P 1/2) transition between the 124Xe and 136Xe isotopes was experimentally determined using the electron-beam ion-trap facility at the National Institute of Standards and Technology. The mass-shift and the field-shift coefficients were calculated with enhanced precision by the relativistic many-body perturbation theory and multiconfiguration Dirac-Hartree-Fock method. The mean-square nuclear charge radius difference was found to be δ〈r 2〉136,124 = 0.269(42) fm2. Our result has smaller uncertainty than previous experimental results and agrees with the literature values.

Testing three-body quantum electrodynamics with trapped Ti20+ ions: evidence for a Z-dependent divergence between experiment and calculation

We report a new test of quantum electrodynamics (QED) for the w (1s2p(1)P(1)→1s(2)(1)S(0)) x-ray resonance line transition energy in heliumlike titanium. This measurement is one of few sensitive to two-electron QED contributions. Systematic errors such as Doppler shifts are minimized in our experiment by trapping and stripping Ti atoms in an electron beam ion trap and by applying absolute wavelength standards to calibrate the dispersion function of a curved-crystal spectrometer. We also report a more general systematic discrepancy between QED theory and experiment for the w transition energy in heliumlike ions for Z>20. When all of the data available in the literature for Z=16-92 are taken into account, the divergence is seen to grow as approximately Z(3) with a statistical significance on the coefficient that rises to the level of 5 standard deviations. Our result for titanium alone, 4749.85(7) eV for the w line, deviates from the most recent ab initio prediction by 3 times our experimental uncertainty and by more than 10 times the currently estimated uncertainty in the theoretical prediction.

Absolute transition frequencies and quantum interference in a frequency comb based measurement of the (6,7)Li D lines

Optical frequencies of the D lines of (6,7)Li were measured with a relative accuracy of 5 × 10⁻¹¹ using an optical comb synthesizer. Quantum interference in the laser induced fluorescence for the partially resolved D2 lines was found to produce polarization dependent shifts as large as 1 MHz. Our results resolve large discrepancies among previous experiments and between all experiments and theory. The fine-structure splittings for ⁶Li and ⁷Li are 10052.837(22) MHz and 10053.435(21) MHz. The splitting isotope shift is 0.599(30) MHz, in reasonable agreement with recent theoretical calculations.

The 3C/3D line ratio in Ni XIX: New Ab Initio theory and experimental results

We report a fully relativistic close-coupling calculation of the electron impact excitation of Ni xix to derive the 3C/3D line intensity ratio, with an uncertainty of 5%. Convergence of the calculation with respect to both channel coupling effects and the many interacting Rydberg series of resonances has been achieved. New measurements in an electron beam ion trap agree with our calculation. We show that the 3C/3D x-ray line ratio depends sensitively on both electron energy and beamwidth in an optically thin plasma. Accounting for this dependence improves the accuracy of the Ni abundance determination in astrophysical sources.

Analysis of broadband x-ray spectra of highly charged krypton from a microcalorimeter detector of an electron-beam ion trap

Spectra of highly charged Kr ions, produced in an electron-beam ion trap (EBIT), have been recorded in a broad x-ray energy band (0.3 keV to 4 keV) with a microcalorimeter detector. Most of the spectral lines have been identified as transitions of B- to Al-like Kr. The transition energies have been determined with 0.2% uncertainty. A semi-empirical EBIT plasma model has been created to calculate a synthetic spectrum of highly charged Kr and to determine a charge state distribution of Kr ions inside the EBIT.

Microlithography by using neutral metastable atoms and self-assembled monolayers

Lithography can be performed with beams of neutral atoms in metastable excited states to pattern self-assembled monolayers (SAMs) of alkanethiolates on gold. An estimated exposure of a SAM of dodecanethiolate (DDT) to 15 to 20 metastable argon atoms per DDT molecule damaged the SAM sufficiently to allow penetration of an aqueous solution of ferricyanide to the surface of the gold. This solution etched the gold and transformed the patterns in the SAMs into structures of gold; these structures had edge resolution of less than 100 nanometers. Regions of SAMs as large as 2 square centimeters were patterned by exposure to a beam of metastable argon atoms. These observations suggest that this system may be useful in new forms of micro- and nanolithography.

Determination of the xenon 6s[3/2](2)-6s'[1/2](0) clock frequency by interferometric wavelength measurements

We have determined the wave number of the optical two-photon clock transition 6s[3/2](2)-6s'[1/2](0) in xenon by interferometrically comparing the wavelengths of the 6s[3/2](2)-6p'[1/2](1) (lambda = 450 nm) and 6s'[(1/2)] (0)-6p'([1/2]) (lambda = 764 nm) transitions with an iodine-stabilized 633-nm He-Ne laser. These measurements determine the frequency of the two-photon transition [4564.610902(13) cm(-1) for (132)Xe] to better than 1 MHz and provide precise values for the isotope shifts and the hyperfine structures of these transitions.

Stray-light suppression with high-collection efficiency in laser light-scattering experiments

We describe an optical system that we constructed to collect a large fraction of fluorescent light emitted isotropically from a cylindrical interaction region. While maintaining an overall detection efficiency of 9%, the system rejects, by more than 12 orders of magnitude, incident laser light along a single axis that intersects the interaction region. Such a system is useful for a wide variety of light-scattering experiments in which high-collection efficiency is desirable, but in which light from an incident laser beam must be rejected without resorting to spectral filters.