Squeezing Phase Diffusion.

We address the use of optical parametric oscillator (OPO) to counteract phase diffusion, and demonstrate phase-noise reduction for coherent signals traveling through a suitably tuned OPO. In particular, we theoretically and experimentally show that there is a threshold value on the phase noise, above which OPO can be exploited to "squeeze" phase noise. The threshold depends on the energy of the input coherent state, and on the relevant parameters of the OPO, i.e., gain and input-output and crystal loss rates.

Real-time dosimetry with Yb-doped silica optical fibres.

Over the years, many efforts have been made to develop radiation detectors to handle the complex issues of small field dosimetry and achieve the increasing accuracy, precision and in vivo dose monitoring required by the new advanced treatment modalities. In this context, interest has surged in the development of sensors based on scintillating optical fibres. In this paper, the near-infrared radioluminescence and dosimetric properties of Yb-doped silica optical fibres, coupled with a laboratory prototype based on an avalanche photodiode, were studied by irradiating the fibres with photons and electron beams generated by a Varian Trilogy accelerator. The performance of the system in standard and small field sizes has also been investigated, comparing the output factor, percentage depth dose and off-axis ratio measurements of the prototypal detector with other commercial sensors, including the Exradin W1 scintillator. The results of this study demonstrate that the drawback due to the stem effect in Yb-doped silica optical fibres can be managed in a simple but effective way by optical filtering. The robustness of the system in complex dosimetric scenarios and the accuracy and precision achieved by Yb-doped fibres in relative dose assessments suggest an effective use of the system for real-time in vivo dosimetry applications.

Innovative method to investigate how the spatial correlation of the pump beam affects the purity of polarization entangled states.

We present an innovative method to address the relation between the purity of type-I polarization entangled states and the spatial properties of the pump laser beam. Our all-optical apparatus is based on a spatial light modulator, and it offers unprecedented control on the spatial phase function of the entangled states. In this way, we demonstrate quantitatively the relation between the purity of the generated state and the spatial field correlation function of the pump beam.

Generation of entangled photon pairs using small-coherence-time continuous wave pump lasers.

We address the generation of entangled photon pairs by parametric downconversion from solid state cw lasers with small coherence time. We consider a compact and low-cost setup based on a two-crystal scheme with type-I phase matching. We reconstruct the full density matrix by quantum tomography and analyze in detail the entanglement properties of the generated state as a function of the crystal's length and the coherence time of the pump. We verify the possibility to improve the visibility using a purification protocol based on a compensation crystal.