We describe a measuring system for determining the state of polarization of a beam of light in terms of its Stokes parameters. The technique which can be fully automated incorporates a monochromator and single photon counting detection and can thus be applied over a large wavelength range for very weak optical signals. Fourier transformation of the data by an on-line minicomputer allows immediate calculation of the Stokes parameters. We discuss special applications to light emitted from excited atomic systems with and without cylindrical symmetry.

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Transition rates, oscillator strengths, and line strengths are calculated for the 49 possible electric-dipole transitions between the eight even-parity 2s2p 2 states and the seven odd-parity 2s 2 2p and 2p 3 states in boronlike ions with nuclear charges ranging from Zϭ6 to 100. Relativistic many-body perturbation theory ͑MBPT͒, including the Breit interaction, is used to evaluate retarded E 1 matrix elements in length and velocity forms. The calculations start from a 1s 2 Dirac-Fock potential. First-order MBPT is used to obtain intermediate coupling coefficients and second-order MBPT is used to calculate transition matrix elements. Contributions from negative-energy states are included in the second-order E 1 matrix elements to ensure gauge independence of transition amplitudes. The transition energies used in the calculation of oscillator strengths and transition rates are from second-order MBPT. Transition rates, line strengths, and oscillator strengths are compared with critically evaluated experimental values and with results from other recent calculations. Lifetimes of the five possible odd-parity upper levels and the five possible even-parity upper levels are given for Zϭ6-100. Trends of the transition rates as functions of Z are illustrated graphically for selected transitions.

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Spectra of highly-ionized silicon, aluminium, sulfur and argon ions produced by the beam-foil technique have been analysed in the 5-40 nm wavelength range. Numerous transitions belonging to n = 3-4, 4-5 and 3-5 transitions arrays in the beryllium-like spectra Al X, Si XI, S XIII and Ar XV were observed for the first time. The assignment of spectral lines was corroborated by comparison along the isoelectronic sequence.