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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We have measured the 6s − 7p 1/2,3/2 transition probabilities in atomic cesium using a direct absorption technique. We use our result plus other previously measured transition rates to derive an accurate value of the vector transition polarizability β and, consequently, re-evaluate the weak charge QW . Our derived value QW = −72.65(49) agrees with the prediction of the standard model to within one standard deviation.

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We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find He"*""""/He"*" = 1.6%±0.3% at /zv==2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Aberg, who predict 1.7%.

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