Effect of the correlation function on the focal shift of a partially coherent beam.

It is known that the focal shift is closely related with the Fresnel number of the lens system, the amplitude, and the spatial coherence of the light beam. In this paper, we investigate the focusing properties of a partially coherent beam with nonconventional correlation function, named a generalized multi-Gaussian correlated Schell-model beam, through deriving the analytical expression for its effective beam width. We find that the focal shift is also affected by the structure parameter of the correlation function. Our results provide a novel way for controlling the focal shift.