Biomedical subjects

Massimo Santarsiero

Publications and source records attributed to Massimo Santarsiero.

14 recordsLinked to original sources

PubMed2006

Phase and amplitude retrieval in ghost diffraction from field-correlation measurements.

We report the results of experiments about the inversion of ghost diffraction with pseudothermal light. A complete retrieval of the complex transmission function of planar transparencies, illuminated by spatially incoherent, quasimonochromatic light, is achieved. This is obtained by measuring the field (instead of the intensity) correlation function. In particular, the determination of the phase of the correlation function is made particularly easy and robust by the use of a suitably modified Young interferometer. The presented results refer to the cases of a clear slit and a phase step.

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PubMed2006

Vector mode analysis of a young interferometer.

It is proved that, when the vector modal theory of coherence is applied to a pair of fixed points, exact results are obtained for the mode structure. In particular, it is shown that the field radiated by the pinholes of a Young interferometer can always be represented by the incoherent superposition of no more than four perfectly correlated and polarized modes. The role of such modes is illustrated through a simple example.

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PubMed2006

Measuring spatial coherence by using a reversed-wavefront Young interferometer.

A very simple optical setup for the measurement of the modulus and the phase of the two-point correlation function of a partially coherent light field is presented. The system consists of a slightly modified version of a Young interferometer and requires a single Young mask in order to determine the correlation function at any pairs of points. Experimental results are presented for the case of a synthesized partially coherent secondary source.

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PubMed2006

Effects of coherence on the degree of polarization in a young interference pattern.

Recent predictions concerning the relationship between the degree of polarization at a typical point of a Young interference pattern and the degree of coherence of the electromagnetic field at the pinholes are tested by a simple experiment. In particular, it is shown that light that is completely unpolarized at the pinholes can become partially polarized across the fringe pattern.

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PubMed2006

Nonparaxial fields with maximum joint spatial-directional localization. I. Scalar case.

In paraxial optics, the spatial and angular localization of a beam are usually characterized through second moments in intensity. For these measures, Gaussian beams have the property of achieving a minimum angular spread for a given spatial spread (or beam waist). For wide-angle fields, however, the standard measures of spatial and angular localization become inappropriate, and new definitions must be used. Previously proposed definitions [J. Opt. Soc. Am. A 17, 2391 (2000)] are adopted, and the scalar monochromatic wave fields that achieve a minimum angular spread for a given spatial spread are found.

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PubMed2006

Nonparaxial fields with maximum joint spatial-directional localization. II. Vectorial case.

The monochromatic nonparaxial vector fields that achieve a minimum spatial spread for a given directional spread are found. The derivation of these fields is analogous to the one presented in part I of this series for the case of scalar fields. This derivation is based on a variational treatment and multipolar expansion. The resulting lower bounds for the spreads of vector fields turn out to be considerably more restrictive than for scalar fields.

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PubMed2006

Joint spatial-directional localization features of wave fields focused at a complex point.

A systematic study of the joint spatial-directional localization features of monochromatic wave fields focused at a complex point is presented, on the basis of recently introduced measures of spatial and directional spread for wide-angle wave fields. Such features are compared with those of a class of fields defined to achieve the theoretical minimum product of these spread measures. It is found that the two classes of fields are remarkably similar.

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PubMed2005

Highly focused spirally polarized beams.

The features of spirally polarized light beams focused by high-numerical-aperture systems are investigated in the nonparaxial regime by means of Debye theory with a multipole expansion technique. General expressions of the expanding coefficients are given, as well as the electric field distributions across the focal plane. Numerical examples are presented for the case of spirally polarized beams of the donut type. Comparisons with recent experimental results are also shown.

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PubMed2004

Shape invariance and a universal form for the Gouy phase.

It is shown that Hermite-Gaussian beams, Laguerre-Gaussian beams, and certain linear combinations thereof are the only finite-energy coherent beams that propagate, on free propagation, in a shape-invariant manner. All shape-invariant beams have Gouy phase of the universal c arctan(z/zR) form, with quantized values for the prefactor c. It is also shown that, as limiting cases, even two- and three-dimensional nondiffracting beams belong to this class when the Rayleigh distance goes to infinity. The results are deduced from the transport-of-intensity equations, by elementary means as well as by use of the Iwasawa decomposition. A pivotal role in the analysis is the finding that the only possible change in the phase front of a shape-invariant beam from one transverse plane to another is quadratic.

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PubMed2004

Nonparaxial propagation of spirally polarized optical beams.

The free-propagation features of light beams whose transverse electric field lines are logarithmic spirals (namely, spirally polarized beams) are investigated in both the paraxial and the nonparaxial regime. The complete propagated electric field is considered, and some general properties are obtained regardless of the specific transverse distribution. Simple and significant analytical results are obtained when the transverse intensity profile is chosen as that pertinent to an axially symmetric Laguerre-Gaussian beam of order 1 (namely, spirally polarized donut beams). In particular, it is found that for such beams, the propagated longitudinal electric field can be expressed as a simple superposition of elegant Laguerre-Gaussian beams. Numerical results are presented for different values of the beam parameters and are compared with recently obtained experimental results.

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PubMed2003

Summing Lax series for nonparaxial beam propagation.

It is shown that the approach proposed by Lax et al. [Phys. Rev. A 11, 1365 (1975)] for studying the propagation of an electromagnetic beam beyond the paraxial approximation can be efficiently employed evenwhen the beam under consideration presents a very nonparaxial character. The method that we present consists of applying a nonlinear resummation scheme, the so-called delta transformation, to the divergent perturbative series arising from the Lax scheme. Numerical results pertinent to the evaluation of transverse and longitudinal components of the electric field are presented for the particular case of vectorial Gaussian beams, showing the effectiveness of the method.

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PubMed2003

Coherent-mode decomposition of partially polarized, partially coherent sources.

It is shown that any partially polarized, partially coherent source can be expressed in terms of a suitable superposition of transverse coherent modes with orthogonal polarization states. Such modes are determined through the solution of a system of two coupled integral equations. An example, for which the modal decomposition is obtained in closed form in terms of fully linearly polarized Hermite Gaussian modes, is given.

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PubMed2003

Evaluation of the spatial coherence of a light beam through transverse intensity measurements.

The problem of recovering the coherence features of a partially coherent quasi-monochromatic scalar optical source, starting solely from intensity measurements on the emitted beam, is addressed in the most general way, under the paraxial approximation. In particular, it is shown that on expanding the beam emitted by the source as a bundle of partially correlated Hermite-Gaussian beams, the correlation coefficients can be recovered, in principle, simply by performing scalar products between transverse intensity distributions and suitably defined functions.

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PubMed2002

Exact axial electromagnetic field for vectorial Gaussian and flattened Gaussian boundary distributions.

The exact expressions of the electromagnetic field pertinent to Gaussian and flattened Gaussian linearly polarized boundary distributions have been derived in closed-form terms for any point lying on the axis. The obtained results allow the fields to be predicted for an arbitrary transverse beam size. Numerical results showing the differences between the exact results and those obtained within the paraxial framework are also presented.

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