Correlation-induced changes of the degree of paraxiality of a partially coherent beam.

The degree of paraxiality (DOP) is a quantification of how paraxial (or nonparaxial) a light field is. In this article, we study the DOP of a partially coherent beam with a nonconventional spatial correlation function and explore the correlation-induced changes of the DOP. Analytical expressions for the DOP and the far-field divergence angle of a generalized multi-Gaussian correlated Schell-model (MGCSM) beam are derived. The properties of the DOP and the far-field divergence angle for the first type and the second type of generalized MGCSM beams without and with truncation in free space are illustrated numerically, and we find that the DOP and far-field divergence angle are closely related with the distribution of the correlation function. Modulation of the correlation function provides a novel way for modulating the nonparaxial properties of a partially coherent beam.