In this contribution I describe the main characteristics of the inversion codes developed at the Instituto de Astrofísica de Canarias for the analisys of Stokes profiles emerging from single (magnetized or non-magnetized) atmospheres and thin flux tubes. Some results of the application of these codes to real data, including infrared Stokes profiles

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Using Hubble Space Telescope and WFPC2 we obtained short exposure images for a hundred of BL Lac objects. The targets were centered mostly in the PC using the F702W filter. Sources from various samples, including objects of very different redshift (0.05 to 1.2), have been observed. The high resolution and homogeneity of the images allow us to

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This paper addresses the problem of scattering line polarization and the Hanle effect in one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) media for the case of a two-level model atom without lower-level polarization and assuming complete frequency redistribution. The theoretical framework chosen for its formulation is the QED