H J Beyer

Progress in atomic spectroscopy

This book presents reviews by leading experts in the field covering areas of research at the forefront of atomic spectroscopy. Topics considered include the k ordering of atomic structure, multiconfiguration Hartree-Fock calculations for complex atoms, new methods in high-resolution laser spectroscopy, resonance ionization spectroscopy (inert atom detection), trapped ion spectroscopy, high-magnetic-field atomic physics, the effects of magnetic and electric fields on highly excited atoms, x rays from superheavy collision systems, recoil ion spectroscopy with heavy ions, investigations of superheavy quasi-atoms via spectroscopy of electron rays and positrons, impact ionization by fast projectiles, and amplitudes and state parameters from ion- and atom-atom excitation processes.

Experimental investigation of the possibility of enhanced photon detection in EPR type experiments

Abstract The polarization properties of the two photons emitted simultaneously in the spontaneous decay of metastable atomic deuterium have been used in an experiment to investigate the possibility of bias or enhancement in the detection process in Einstein-Podolsky-Rosen (EPR) type experiments. No evidence of enhancement has been found.

A study of the 4p-excited autoionization resonances in Sr by measurement of the angular correlation between the photoejected electrons and polarized fluorescent photons

For five autoionization resonances of Sr in the 4p excitation region, we have determined the ratios of five amplitudes and one phase difference for the photo-ejected electron waves which leave the ion in the excited states. The technique employed is a combination of conventional angle-resolved photoelectron spectroscopy, and angular correlation measurements between photoejected electrons and polarized fluorescent photons. We discuss how the ratios of the dipole amplitudes are related to the spectroscopic descriptions of the resonances studied.

A new approach to the complete photoionization experiment, by means of a coincidence measurement between autoionized electrons and polarized fluorescent photons, in the region of the 3p-3d resonance in calcium

By using synchrotron radiation to excite calcium atoms in the 3p-3d resonance region, excited calcium ions are generated. In the first measurement of this kind, we have measured the polarization of the fluorescent photons which result from the decay of these ions, in coincidence with the corresponding angle-resolved photoejected electrons. By combining this with the angular distribution parameter for these same electrons, measured in a separate experiment, we are able to calculate for this specific case, within the assumption of LS coupling, the ratio of the dipole amplitudes for the outgoing waves and their phase difference.

Fluorescence from excited states of Ca+ and Sr+ following photoionization

The simultaneous photoionization and excitation of Ca and Sr atoms from the ground state into the first excited ionic P state has been investigated by measuring the intensity and the polarization of the emitted fluorescence radiation at 3933 AA and 4078 AA respectively. Cross sections for the direct excitation of the Ca+(42P) and Sr+(52P) states were found to be extremely small ((10-19 cm2 at threshold). However, these states can also be populated by resonant photoexcitation of atomic inner-shell states in the region of the Ca(3p64s2-3p53d4s2) transition at 394.8 AA and the Sr(4p65s2-4p54d5s2) transition at 490.9 AA, followed by autoionization processes. The ionic fluorescence in the respective resonance regions of Ca and Sr has been measured and compared with the corresponding photoelectron and photoion spectra.

Angular correlation measurement between the photo-excited autoionized electron and subsequent polarized fluorescent photon at an autoionization resonance of Sr

We demonstrate that the technique of measuring the angular correlation between the photoejected electron and polarized fluorescent photon can be used to determine all the photoionization parameters for the relativistic case. Applying this technique to an autoionization resonance of atomic Sr, values were obtained for the ratios of the three dipole amplitudes and the two phase differences.

Dipole matrix elements for 4p photoionization of Sr

Measurements of the angular distribution of photoelectrons and the associated Auger electrons, together with their angular correlation, have allowed the relative amplitudes and phases of the s and d matrix elements for 4p3/2 photoionization of Sr to be determined. The results indicate that there is destructive interference between the s and d channels and that the photoionization parameters show little dependence on energy.

A new approach to the complete experiment of atomic photoionization

Abstract A summary of our measurements of fluorescence polarization and photoelectron angular distributions on the Ca atom is given. The need for coincidence measurements in order to provide reliable values of dipole moment ratios and phase differences is established. We have investigated the circular polarization properties of the invident light, and as a result have improved the accuracy of our earlier determinations of the dipole moment ratio and phase difference.

Polarisation correlation measurements on the 31P state of helium for positive and negative scattering angles

The scattering amplitudes for electron impact excitation of the 31P state of helium have been measured for an incident energy of 80 eV and both positive and negative electron scattering angles using polarisation correlations between inelastically scattered electrons and 501.6 nm photons. The expected dependence of the Stokes parameters on the sign of the electron scattering angle is considered and found to agree with the present measurements which differ from the earlier results of Standage and Kleinpoppen (1976) in the symmetry behaviour of the linear Stokes parameter P2.

Two-Photon Polarization Fourier Spectroscopy of Metastable Atomic Hydrogen

For many years the theoretical and experimental study of atomic hydrogen has been used to improve our understanding and extend our knowledge of the fundamental properties and behaviour of atoms. The states with principal quantum number n=2 are and have been of special interest and importance, in particular with regard to the determination of the fine structure constant and measurement of the Lamb shift. It was, of course, the observations of the Lamb shift in 1947 and 1950 by Lamb and Retherford [1] which, by demonstrating the nondegeneracy of the 22S½ and 22P½ states, confirmed that the 22S½ state would be metastable in experimentally realisable situations, and showed that it should be possible to observe the two-photon emission which is the main mode of decay of this state. However, Goppert-Mayer, in 1931, in a paper [2] which pioneered the field of multiphoton transitions, was the first to predict the possibility of the spontaneous two-photon decay process and, in 1940, Breit and Teller [3] applied this theory to the 22S½ − 12S½ transition in atomic hydrogen. Improved calculations of the characteristics of the two-photon decay process were carried out by Spitzer and Greenstein [4], Shapiro and Breit [5], Zon and Rapaport [6], Klarsfeld [7] and Johnson [8]. Further refinements to the theory have been made for example by Goldman and Drake [9], Parpia and Johnson [10], Tung et al [11], Florescu [12], Costescu [13] and Drake [14]. A comprehensive review concerning the metastability of atomic hydrogen up to 1969 was given by Novick [15] in which he emphasised the various controversies with regard to the metastability or otherwise of the 2S state during the first part of this century.