Walter Neu

Double-pulse technique for optical emission spectroscopy of ablation plasmas of samples in liquids

Sharp atomic and ionic line spectra of excimer-laser-induced ablation plasmas of samples in liquids were observed. A new double-pulse technique employing quartz fibers facilitates spectral analysis of samples in liquids in which spectral lines normally are strongly broadened and quenched. The first pulse generates a cavitation bubble on the sample surface, which provides a gaseous environment for optical emission spectroscopy on the ablation plasma induced by a second pulse fired into the bubble.

Nuclear spin and magnetic moment of 11Li

Abstract Nuclear spin and magnetic moment of 11Li have been measured by optical pumping of a fast atomic beam. The angular asymmetry of the β-radiation from the polarized nuclei was used to detect the hfs of the 2s 2 S 1 2 −2 p 2 P 1 2 resonance line and the NMR signal cubic LiF crystal lattice. The results I= 3 2 and μI=3.6673(25) n.m. indicate a pure 1p 3 2 state of the valence proton.

Xenon isotopes far from stability studied by collisional ionization laser spectroscopy

Abstract The new collisional ionization scheme in collinear laser spectroscopy has enabled the study of hyperfine structures and isotope shifts of xenon isotopes over the large mass range A = 116−146. The sensitivity of this method is demonstrated by the discovery of 146 Xe. Mean square charge radii, and spins and moments of the neutron-rich isotopes 137,139,141,143 Xe are deduced and discussed in comparison with earlier results on barium.

Optical laser spectroscopy and hyperfine structure investigation of the 102S, 112S, 82D, and 92D excited levels in francium

The authors present an extension to low-lying states of francium (10s, 11s, 8d, 9d) of a previously published high-resolution experiment performed on the ns and nd Rydberg levels. These four levels were investigated at CERN with the on-line mass separator ISOLDE using stepwise laser excitation in collinear geometry. Accurate energy measurements lead to a more reliable determination of the quantum defects of the whole ns and nd series, together with the ionization potential for 212Fr (nuclear spin I=5) which is found to be 32848.872 (9) cm-1. The measurement of the fine structure splittings for the nd 2D3/2, 5/2 doublets was completed at the same time. The main result of the study is the first observation and measurement of hyperfine structures in 2S and 2D states.

Nuclear ground state properties of 99Sr by collinear laser spectroscopy with non-optical detection

Collinear fast-beam laser spectroscopy, with improved sensitivity for ions with hyperfine split transitions, is performed to measure the hyperfine structure and the isotope shift of the well deformed short-lived 99Sr. The new method consists in ground state depopulation by a two-step optical pumping sequence prior to state selective neutralization and fast-atom counting. A definitive nuclear spin value I = 32, the change in mean square charge radius δ〈r2〉98,99 and the nuclear moments are derived. These results are compared to nuclear spectroscopy information and are interpreted in the frame of the particle plus deformed core model.

Quadrupole moments of radium isotopes from the 7p2P3/2 hyperfine structure in Ra II

The hyperfine structure and isotope shift of221–226Ra and212,214Ra have been measured in the ionic (Ra II) transition 7s2S1/2–7p2P3/2 (λ=381.4 nm). The method of on-line collinear fast-beam laser spectroscopy has been applied using frequency-doubling of cw dye laser radiation in an external ring cavity. The magnetic hyperfine fields are compared with semi-empirical and ab initio calculations. The analysis of the quadrupole splitting by the same method yields the following, improved values of spectroscopic quadrupole moments:Qs(221Ra)=1.978(7)b,Qs(223Ra)=1.254(3)b and the reanalyzed valuesQs(209Ra)=0.40(2)b,Qs(211Ra)=0.48(2)b,Qs(227Ra)=1.58(3)b,Qs(229Ra)=3.09(4)b with an additional scaling uncertainty of ±5%. Furthermore, theJ-dependence of the isotope shift is analyzed in both Ra II transitions connecting the 7s2S1/2 ground state with the first excited doublet 7p2P1/2 and 7p2P3/2.

ISOTOPE SHIFT AND HYPERFINE STRUCTURE OF STABLE PLATINUM ISOTOPES

Isotope shift (IS) and hyperfine structure (hfs) measurements have been performed on seven lines of the platinum I spectrum with interference as well as laser fluorescence spectroscopy. In the latter case a frequency-doubled single-mode cw dye laser was applied. The IS of190Pt with a natural abundance of only 0.01% was determined to beδν190, 192=−38.65(8) mK in theλ306.47 nm transition. The IS parameters and the effective hfs integrals in the configuration (5d+6s)10 were determined in intermediate coupling by a least squares fit of the IS and hfs data with eigenvectors obtained from the platinum fine structure (fs). The results are compared with theoretical values and yield improvedδ〈r2〉 data.

Nuclear moments of strongly deformed strontium isotopes

Nuclear spins, moments and mean square charge radii of78–100Sr have been obtained by fast ion-beam collinear laserspectroscopy. The experiments performed at ISOLDE have been extended to include99Sr, measured by a non-optical detection scheme with a two-step optical pumping sequence. The results for the strongly deformed isotopes are discussed in the frame of the particle-plus-deformed core model.

Reduction of photodegradation in optical fibers for excimer laser applications

Power transmission of excimer laser radiation at 308 nm through waveguides is of growing importance in medical applications. The maximum energy densities achievable at distal fused silica optical fiber ends are limited by the surface damage threshold of fused silica and by photodegradation of the optical fiber material. Limitations due to the surface damage threshold at the front surface can be avoided by applying tapered fiber geometries. In order to minimize photodegradation effects color center formation caused by high energy UV radiation has to be reduced. This involves optimization of the fused silica material properties and the necessity of modifying the manufacturing processes. Measurements on all silica fibers at 308 nm wavelength (XeCl excimer laser) show different influences of core material manufacturing. Not only the overall decrease of transmission but also the dependence of transmission changes on the number of laser pulses and defect annealing are strongly affected. Consequences for improved performance of all silica optical fibers in angioplasty are demonstrated by measurements on specially produced samples.

Elaboration of excimer lasers dosimetry for bone and meniscus cutting and drilling using optical fibers

In order to optimize bone and cartilage ablation, various excimer laser systems at 308 nm wavelength (pulse width 28 ns, 60 ns, 300 ns) and tapered fibers (core diameter 400 micrometers , 600 micrometers , 1000 micrometers ) were combined. By varying the major parameters such as fluence, pulselength, repetition rate, fiber diameter, medium, manner of application (drilling, cutting); analysis was made of the interaction of the excimer laser beam with different organic material (meniscus, bone tissue). More than 300 cuts and drillings have been realized with different parameters. The ablation rate mainly depends on fluence, repetition rate and pulse duration. The achieved ablation rate was 3 micrometers /pulse in bone. The drilling speed of the meniscus was 6 mm/s. The samples showed no carbonization at all, when being cut or drilled in liquid medium. This might be a breakthrough in fiber guided excimer laser surgery. From these and further experiments the authors obtained the dosimetry, which will be the basis for the elaboration of necessary operation guidelines for accident surgery.