Focusing of partially coherent Bessel-Gaussian beams through a high-numerical-aperture objective.

The focusing properties of partially coherent Bessel-Gaussian beams passing through a high-numerical-aperture objective are studied based on vectorial Debye theory. Expressions for the intensity distribution, degree of coherence |mu|, and degree of polarization P are derived near the focus. Numerical calculations are performed to analyze the influences of varying corresponding parameters on the intensity distribution, |mu|, and P in the focal region. It is shown that the intensity, |mu|, and P in the focal region are all influenced by varying the effective coherent length L(c) of incident beams and maximal angle alpha determined by the numerical aperture of the objective. Also, the linearly polarized incident field is found to be depolarized after it is focused by a high-numerical-aperture objective.