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Quantum states of twin photons entangled in angular momentum and polarization provide new degrees of freedom to researchers in quantum information and imaging. This work discuss these states and also emphasizes differences between two proposed models for twin photons entangled in angular momentum. Answers to the presented questions would contribute to a better understanding of this nonlinear process.

Among interference effects that have been observed using parametric down-conversion light, some experiments show that second and fourth order interference effects can be observed between independent light beams. Also, it has been shown that the presence of mirrors reflecting the pump and the down converted beams can give rise to interference effects. In this paper we show that these mirror effects can be explained alternatively by means of a coherence induced between initially independent beams. Our analysis is based on a longitudinal multimode approach and leads to intensity and coincidence distributions and fringe visibilities. We also present experimental results showing that mirror effects can be observed even using a pump beam with a coherence length much smaller than the distance between crystal and pump mirror.

A discussion is presented of the response of a Fabry-Perot cavity to a single-photon wavepacket generated by the down-converted luminescence (signal beam) and a delayed coincidence measurement between this wavepacket propagated through the cavity and its conjugated idler beam. This time-domain measurement is done in the non-interfering regime, that is, when the coherence length of the incoming signal wavepacket is shorter than the distance between the mirrors. That provides a measurement of the flight time of the wavepacket inside an optical cavity, alternative to the more usual schemes.

Summary form only given. This work analyzes patterns seen when a signal beam of spontaneous parametric downconverted light illuminates a double-slit (Young) and a coincidence pattern ("object") appears on scanning behind the double-slit arrangement and, conversely, when the conjugated idler beam is scanned spatially keeping the signal detector fixed and a "Young" coincidence pattern ("image") is revealed. Mandel's theory for downconversion is applied, in the (r)-space, to this analysis.

Diffusion of FeCl 2 ·4H 2 O in glycerol (0.4 M) is measured from 20 to 60°C through light scattering experiments. In this temperature range the solvent viscosity varies by a factor of 20. The scattering angle is varied from 30 to 150° to show the hydrodynamic q −2 behavior in the scattering wavevector q . Assuming a Stokes—Einstein relationship D = k B T /6πη R , the radius R = 2.05 ± 0.09 A is obtained for ferrous chloride.

The experimental results of measurements of the temperature dependence of the Raman cross-sections of SrTiO3 and BaTiO3 in the temperature regions of 25–600 and 25–300°C respectively are presented. A controversial question about an anomalous temperature dependence of the cross-sections which would be related to a possible order-disorder transition in those materials is resolved. The intensity anomaly is shown to be related to a lowering of the effective absorption edge with increasing temperature which produces losses both at the laser and Raman frequencies.