J. M. Movilla

Parametric characterization of the spatial structure of non-uniformly polarized laser beams

We present an approach for describing the spatial structure of partially polarized light fields. Unlike the treatments usually encountered in the literature, in which the polarization state is represented by position-dependent functions, the formalism shown here characterizes the polarization by means of a family of measurable overall parameters averaged over the transverse spatial region where the beam intensity reaches significant values. Generalized degrees of polarization are introduced to evaluate the uniformity of the spatial distribution of the polarization state of the beam-like field. The possibility of improvement and optimization of the quality of a polarized laser beam (understood as the general usefulness of such field for collimation and focussing) is analyzed by employing first-order optical systems. Finally, attention is briefly devoted to non-paraxial electromagnetic vector beams, whose parametric description of their polarization properties constitutes, at present, a challenge for theoreticians.

Orbital angular momentum of partially coherent beams

The definition of the orbital angular momentum established for coherent beams is extended to partially coherent beams, expressed in terms of two elements of the beam matrix. This extension is justified by use of the Mercer expansion of partially coherent fields. General Gauss-Schell-model fields are considered, and the relation between the twist parameter and the orbital angular momentum is analyzed.

Parametric characterization of non-uniformly polarized beams

A new overall parameter is defined, namely, the generalized degree of polarization, which involves the spatial distribution of the polarization of a light beam. This parameter is introduced on the basis of a general treatment recently proposed [Optics Lett. 22 (1997) 206] to characterize partially polarized fields, which extends the Stokes-Mueller formalism to describe the intensity moments of a quasimonochromatic beam. The main properties and the physical meaning of this parameter with regard to the spatial inhomogeneities of the polarization state are analysed, and a general measurement procedure is proposed.

SPATIAL CHARACTERIZATION OF GENERAL PARTIALLY POLARIZED BEAMS

The spatial characterization of light beams given in terms of intensity moments is extended to partially polarized beams by means of a generalization of the Stokes-Mueller formalism. A simple classification scheme of partially polarized fields is proposed, and laws of propagation through nonpolarizing and polarizing optical systems are provided. Some invariant parameters are also investigated.

Degree of polarization of non-uniformly partially polarized beams: a proposal

Two overall parameters are proposed to characterize the degree of polarization and its uniformity across the transversal section of non-uniformly partially polarized beams. Such parameters can be measured according to the well-known standard methods used to obtain the Stokes parameters, with the addition of a CCD camera to determine the beam intensity at each point of the observation plane.

Beam propagation through uniaxial anisotropic media: global changes in the spatial profile.

The propagation of electromagnetic beams through uniaxial anisotropic media is investigated. The Maxwell equations are solved in the paraxial limit in terms of the plane-wave spectrum associated with each Cartesian field component. Attention is focused on the global changes in the spatial structure of the beam, which are described by means of the second-order intensity moment formalism. In particular, the propagation law for the intensity moments through this kind of media is obtained. As a consequence it is inferred that it is possible to improve the beam-quality parameter by using these media.

Beam quality of partially polarized beams propagating through lenslike birefringent elements

Changes generated by lenslike birefringent elements on the beam-quality parameter of partially polarized beams are investigated. Analytical expressions for the beam-quality gain at the output of such systems are given in terms of the second-order intensity moments of the field. Explicit conditions to improve and optimize the beam-quality parameter after propagation through these birefringent transmittances are also shown.

Quality improvement of partially polarized beams

Improvement of the beam-quality parameter of partially polarized beams is investigated. We focus on the use of a Mach-Zehnder-type interferometric arrangement with crossed polarizers. The analysis has been carried out within the framework of the intensity moment formalism. Conditions are given under which the beam-quality parameter is optimized.

On the measurement of the generalized degree of polarization

On the basis of well-known methods to obtain the standard Stokes parameters, two simple experimental procedures are analysed to measure the so-called generalized degree of polarization, P, defined elsewhere [Opt. Commun., 149 (1998) 230]. After discussing the accuracy of the methods, the generalized degree of polarization of a non-uniformly polarized beam emerging from an optically pumped birefringent Nd:YAG rod optically pumped is experimentally investigated in terms of the pumped power.

Beam-quality optimization of partially polarized fields

For light fields propagating through rotationally symmetric first-order optical systems, the possibility of improvement of the beam-propagation factor is shown to arise when the vectorial behavior is taken into account. For partially polarized beams, we find the optimized value of the beam-quality parameter that can be attained by using this kind of system. This value is given in terms of the beam qualities associated with the transverse polarization components of the vector field. On the basis of the so-called intensity-moment formalism, the general conditions that should be fulfilled at some plane to reach such an optimized value are determined. A procedure to experimentally get the optimization conditions is also proposed.