P E G Baird

Measurement of the 1s-2s energy interval in muonium

The 1s-2s interval has been measured in the muonium (&mgr;(+)e(-)) atom by Doppler-free two-photon pulsed laser spectroscopy. The frequency separation of the states was determined to be 2 455 528 941.0(9.8) MHz, in good agreement with quantum electrodynamics. The result may be interpreted as a measurement of the muon-electron charge ratio as -1-1.1(2.1)x10(-9). We expect significantly higher accuracy at future high flux muon sources and from cw laser technology.

A MEASUREMENT OF THE 1S-2S TRANSITION FREQUENCY IN MUONIUM

Doppler-free two-photon laser spectroscopy has been employed to measure the 12S12−22S12 transition in the muonium atom (μ+e−). A value of 2 455 529 002(33) (46) MHz has been obtained, which agrees with QED calculations within two standard deviations. The Lamb shift contributions are tested to the level 8×10−3. The corresponding measurements in hydrogen and deuterium using the same apparatus and laser system provide a test of the applied systematic corrections and have verified the systematic error of 46 MHz quoted. The mass of the positive muon has been derived from the isotope shift in this transition and yields a value of 105.65880(29)(43) MeVc2.

The Faraday effect and magnetic circular dichroism in atomic bismuth

The authors give the theory of optical Faraday rotation and circular dichroism for a transition of mixed magnetic-dipole and electric-quadrupole character in the presence of hyperfine structure. The results are applied to two transitions of atomic bismuth, lambda 647.6 nm (Jj=3/2 to Jj=5/2) and lambda 875.5 nm (Jj=3/2 to Jj=3/2). They have studied the Faraday rotation profiles of these lines under high resolution; the results confirm the theoretical predictions and for each transition give a value for the ratio, chi , of the electric-quadrupole and magnetic-dipole reduced matrix elements, (Jj//( omega /4 square root 3)(-2er2C(2))//Ji) and (Jj// mu //Ji). They obtain chi =-0.60(2) for lambda 647.6 nm and chi =+0.13(7) for lambda 875.5 nm, to be compared with the theoretical values -0.65 and +0.11 respectively.

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.

Theory and observation of Faraday rotation obtained with strong light fields

The authors have observed dramatic changes in both the magnitude and the lineshape of Faraday rotation on an allowed E1 transition in Sm I (4f 66s2 7F0-4f 66s6p 7G1) as a function of laser intensity and buffer-gas pressure. The effect is ascribed to the development of optical and Zeeman coherences and a theoretical treatment, based on the solution of steady-state density matrix equations is given. Effects of optical pumping on the odd isotopes 147Sm and 149Sm, both with I=7/2, are also considered.

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.

Non-linear Faraday rotation on simple transitions in samarium vapour

New results demonstrating the dramatic changes to the form and magnitude of the resonant Faraday rotation with laser intensity, buffer gas pressure and magnetic field strength are presented for the transitions 4f 66s2 7F0-4f 66s6p 5D1 at 621 nm and 4f 66s2 7F1-4f 66s6p 5D0 at 654 nm. For both transitions, exact analytical solutions to the steady-state density matrix equations are possible and have been used. The experimental results show good qualitative agreement with the theoretical predictions. In the case of the 654 nm line Zeeman coherence occurs in the ground state and can be achieved at lower laser intensities than for the 621 nm line under comparable conditions.

A measurement of parity non-conserving optical rotation in atomic lead

We report a measurement of parity non-conserving (PNC) optical rotation in the vicinity of the 1.279 magnetic dipole transition in atomic lead. We obtain a value for the conventional parameter, , with limits on the nuclear spin-dependent contribution set by the anapole constant . The experimental results, when combined with the relevant atomic calculations, lead to a value for the mass of the boson or, alternatively, place a limit on physics beyond the standard model through the isospin-conserving parameter, S.

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.