Controlling the degree of polarization of partially coherent electromagnetic beams with lenses

We show theoretically that the degree of polarization of a partially coherent electromagnetic beam changes dramatically as the beam is being focused. A low numerical aperture lens can considerably enhance the degree of polarization at its geometrical focus. When two identical lenses are employed in a 4f configuration, the degree of polarization of a beam can be tailored by using amplitude masks in the Fourier plane located in the middle of the two lenses. Our findings open up the possibility to control this fundamental property of random beams in a simple manner