H. Di Lorenzo Pires

Spatial Schmidt modes generated in parametric down-conversion

This paper presents the general spatial Schmidt decomposition of two-photon fields generated in spontaneous parametric down-conversion (SPDC). It discusses in particular the separation of the radial and azimuthal degrees of freedom, the role of projection in modal analysis, and the benefits of collinear phase mismatch. The paper is written in a review style and presents a wealth of numerical results. It aims at emphasising the physics beyond the mathematics, through discussions and graphical representations of key results. The two main conclusions of the paper are the finding of a better law to describe the effective dimensionality of the spatial part of the total Hilbert space and a possible novel feature of the radial Schmidt modes.

Measurement of the orbital angular momentum spectrum of partially coherent beams

In this work we implement a Mach-Zehnder interferometer with an image rotator in one of its arms to measure the orbital angular momentum (OAM) spectrum of a partially coherent beam. By measuring the visibility of the interference as a function of the angle of rotation, the OAM distribution can be recovered via a Fourier transform. Theoretical calculations based on the coherent mode decomposition of the cross-spectral density are in excellent agreement with the experimental data.

Measurements of spatial coherence of partially coherent light with and without orbital angular momentum

We study the spatial coherence of a partially coherent beam before and after being transmitted through a spiral phase plate that changes the overall orbital angular momentum of the field. The two-point coherence function is measured and directly visualized on a CCD through interference in a Mach-Zehnder interferometer equipped with an image rotator. We show, in particular, how the coherence singularities associated with Airy rings are strongly affected by the spiral phase plate.

Near-field correlations in the two-photon field

We experimentally demonstrate intriguing fine structures in the two-photon field that reflect the (near-field) spatial correlations within the SPDC-generated photon pairs. These structures exhibit among others a surface-enhanced two-photon yield and spatial antibunching.

On the statistics of the entropy-depolarization relation in random light scattering

We analyze an apparent disagreement between simulational and experimental results in a recent work of Puentes et al. [Opt. Lett., 30(23):3216, 2005] on the universality in depolarized light scattering. We show that the distribution of experimental points in the allowed region of the index of depolarization versus entropy diagram is ultimately determined by the statistics on the Mueller matrices, rather than on the eigenvalues of an associated Hermitian matrix. We propose a reasonable criterion that distinguishes the class of physically admissible from the physically realizable scattering media. This strategy yields further insight into the depolarization properties of media.