G K Woodgate

Laser spectroscopy of calcium isotopes

Improved measurements of isotope shifts in the 4s2 1S0-4s5s 1S0 transition of calcium are reported for the stable isotopes. A comparison with isotope shift measurements in other transitions by means of a King plot shows satisfactory agreement. Values of the changes in mean-square nuclear charge radius delta (r2) from a combined analysis of muonic isotope shifts and electron scattering data are used to separate the mass and field shifts in the optical lines. This procedure leads to values of delta (r2) for the calcium isotopes from 40Ca to 48Ca using all available high-precision data. The results for delta (r2)A,40 are 3.2(2.5), 215.3 (4.9), 125.4 (3.2), 283.2 (6.4), 118.8 (5.9), 124.2 (5.0), 5 (13) and -4.4(6.0)*10-3 fm2 for A=41 to 48 respectively. Values of the electronic factors relating the observed shifts of delta (r2) are deduced, and discussed in terms of configuration mixing in calcium.

A reformulation of the theory of field isotope shift in atoms

The theory of the field isotope shift (FS) in atomic spectra is discussed critically and the results are presented in a form which is more straightforward than the expressions traditionally used to interpret experimental data. First-order perturbation theory is applied within the single-particle framework to the case of an s or p1/2 electron outside closed shells. Parameters to take account of many-body effects are subsequently included. The nuclear and electronic dependences of the FS are separately discussed. In a generalisation of the work of Seltzer (1986), it is shown that the former can be represented as a series of even charge moments: the coefficients of the first three terms for an s electron are given. The difference between the series for an s and a p1/2 electron is shown to be generally insignificant. The electronic dependence enters through the (relativistic) probability density N of the electron at the origin; for the case of an s electron. They relate N to the magnetic hyperfine splitting factor alpha s. A table which allows N to be found from a measurement of alpha s is given. Second-order field shifts are of the order of 10-3-10-4 of the first-order shifts for a two-neutron change.

Isotope shift in xenon by Doppler-free two-photon laser spectroscopy

Isotope shifts and pressure broadening have been measured in the two-photon transition at 249 nm from the 5p6 1S0 ground level of neutral xenon to a J=0 level of the 5p56p configuration (the 2p5 level in Paschen notation). A continuous-wave tunable dye laser operating at 498 nm with intracavity frequency doubling excited the transition. The work is the first application of Doppler-free laser spectroscopy to a transition involving the ground level of a rare gas. The results show that although no s electron is directly involved in the transition, the field isotope shifts are comparable with those observed in transitions of the type 6s-np.

Laser spectroscopy of the tin isotopes

Isotope shifts of all the stable isotopes and the hyperfine splittings of 115Sn, 117Sn and 119Sn have been measured in the transitions 5s25p23P0-5s25p6s3P1 at 286 nm in Sn I. Tin atoms in a collimated beam to reduce the Doppler width were excited by radiation at 286 nm generated by frequency doubling the light from a CW ring dye laser. Spectra were recorded by monitoring the subsequent decay and calibrated by optical heterodyning. The relative positions of the isotopes are, in MHz: 112; 0.0(1.0), 114;319.5(1.3), 115;412.7(1.1), 116;640.0(0.6), 117;746.8(0.7), 118;945.2(0.7), 119;1039.3(1.1), 120;1214.4(0.5), 122;1448.5(0.7), 124;1656.0(0.7). The bracketed uncertainties are added in quadrature to give the errors of the isotope shifts. For odd-even shifts involving 112, 114, 120, 122 and 124 an extra 0.5 MHz must be added in quadrature. The hyperfine splitting factors of 5s25p6s3P1 are, in MHz: A(115)=-4395.4 (2.1), A(117)=-4790.71(1.7), A(119)=-5014.8(1.9). The results are interpreted in terms of the electronic and nuclear properties of the tin isotopes.

Isotope shift and hyperfine structure for a valence s electron

The authors show that it is valid to use the value of the non-relativistic quantity mod psi (0) mod 2 obtained from a measurement of hyperfine structure (HFS) in the interpretation of field isotope shifts (FS) using conventional theory, in so far as both effects are directly due to a valence s electron interacting with the nucleus. They calculate directly from the Dirac equation the ratio R=FSHFS/ for a simple nuclear model, assuming the potential close to the nucleus to be Coulombic. They discuss the approximations involved, and obtain numerical results for a range of nuclei. Since they are evaluating a ratio they avoid the need to normalise the Dirac wavefunction, the step which leads to the introduction of mod psi (0) mod 2 in the usual treatment. However, this step gives rise to no error in the value of R obtained from the conventional expressions since the normalisation has been carried out in the same way in the two cases. This conclusion is supported by the agreement of the new values of R with those derived from published calculations. Their values of R also agree to within about 1% with those they have obtained using wavefunctions derived from a relativistic self-consistent field program, showing the validity of the Coulomb approximation.

Fine structure and isotope shift of tritium in the Balmer-α transition

By means of saturated absorption spectroscopy in a discharge tube containing hydrogen isotopes, fine-structure intervals in the Balmer- alpha line of tritium have been measured, and for each of four components of that line the tritium-hydrogen and tritium-deuterium isotope shifts have been measured. The results agree with theory within the experimental limits of error, which are typically +or-2 MHz. The profiles of the components of Balmer- alpha have been analysed in detail and in particular a Stark-induced crossover signal has been revealed.

Isotope shift in calcium by two-photon spectroscopy

Isotope shifts between the stable isotopes of calcium have been measured in the transition 4s2 1S0-4s5s 1S0 by the method of two-photon laser spectroscopy. The relative positions of the isotopes are (in MHz): 40Ca, 0.00(27); 42Ca, 606.33(7); 43Ca, 906.32(5); 44Ca, 1169.99(4); 46Ca, 1704.33(70); 48Ca, 2193.49(5).

A comparison of the frequencies of the 1S-2S and 2S-4P transitions in atomic hydrogen

The difference between the frequency of the 2S-4P1/2 transition and a quarter of the 1S-2S transition frequency in atomic hydrogen has been measured by high-resolution laser spectroscopy. The result is 4696.3 (2.0) MHz, from which the value 8168 (8) MHz is derived for the 1S Lamb shift. This is the first determination of this quantity from continuous wave spectroscopy without frequency standards.

Precision cw Laser Spectroscopy of Hydrogen and Deuterium

The 1S–2S transition of atomic hydrogen has attracted considerable attention because of its extremely narrow natural width (1 Hz). High resolution Doppler-free spectra of this transition, obtainable by two-photon absorption, offer the prospect of precise tests of bound-state quantum electrodynamics (QED) and more accurate values for fundamental constants /1/. The two-photon absorption was first observed by HANSCH et al. /2/ at Stanford, in the first of a series of progressively more accurate measurements /3/. Their latest result is a measurement of the IS Lamb shift in hydrogen using continuous-wave radiation /4/.

High precision CW laser measurement of the 1S−2S interval in atomic hydrogen and deuterium

We have excited the 1S‐2S transition in atomic hydrogen and deuterium by two‐photon absorption of cw 243 nm light. The transition frequency has been measured by comparison with calibrated lines in the spectrum of the 130Te2 molecule, providing new precise values for the 1S Lamb shifts or the Rydberg constant.