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We consider the separation of the total angular momentum of the electromagnetic field into a .spin>> and an <> part. Though this separation is normally considered to be unphysical and not observable, we argue that both members in the separation are separately measurable quantities. However, the commutation relations for the associated quantum operators reveal that neither of them is an angular-momentum operator.The angular momentum J of the classical electromagnetic field is defined by [l] J = Eojdrr x [ E x B ] .

We present a theoretical analysis of the intensity correlations between the spectral components of the resonance fluorescence triplet while allowing for detection time differences that are smaller than the inverse frequency width of the frequency filter. Explicit expressions are derived for the intensity correlation functions that are valid for all times. Furthermore, we present the results of measurements on these correlation functions for the 'So~'P& resonance transition of natural barium. In general, the results confirm the theoretical predictions.

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We calculate the reflection coefficient for a light beam incident on the interface between a dielectric and a resonant atomic vapor to 6rst order in the dipole polarization in the vapor. The angle of incidence and the polarization direction are chosen arbitrarily, and saturation is fully accounted for. The atoms are supposed to get deexcited at collisions with the surface. The resulting transient behavior of atoms leaving the surface is responsible for a nonlocal response. This spatial dispersion near the surface is known to produce a natural-linewidth-limited resonance in the vapor reflection coefficient at normal incidence. Our analysis shows that this sub-Doppler structure is broadened by the residual Doppler efFect for non-normal incidence. This structure disappears at the critical angle for total internal reflection, where one predicts a conventional Voigt-type dispersion response, based on the complex-refractive-index approach. We also calculate the saturation broadening of the atomic response for large intensities. Beyond the critical angle, the spectral response suddenly shifts from dispersion to absorption line shapes. In the case of total internal reflection, the spatial dispersion leads to an additional Lorentzian broadening, which results from an effective imaginary Doppler shift at passage through the evanescent wave (transit-time broadening)Ĩ

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We propose a novel setup to investigate the entanglement of orbital angular momentum states living in a high-dimensional Hilbert space. We incorporate noninteger spiral phase plates in spatial analyzers, enabling us to use only two detectors. The two-photon states that are produced are not confined to a 2 x 2-dimensional Hilbert space, and the setup allows the probing of correlations in a high-dimensional space. For the special case of half-integer spiral phase plates, we predict that the Clauser-Horne-Shimony-Holt-Bell parameter S is larger than achievable for two qubits (S=2 sqrt[2]), namely, S=31 / 5.