  Spectral electromagnetic Gaussian Schell-model (SEGSM) beam is a
generalization of Gaussian Schell model beam having parameters with spectral
dependence, which offers a basic classical model for random electromagnetic
wide-sense statistically stationary beam-like fields. We study degree of
polarization (DOP) of a SEGSM beam passing through 2-f and 4-f lens systems. It
is observed that for a 2-f lens system, the spectral DOP at the back focal
plane of the lens changes with respect to the transverse position from the
optic axis, and the spectral parameters of the beam. For a 4-f lens system, the
spectral DOP at the back focal plane is independent of the transverse position
of the beam, whereas it depends on the beam parameters such as mean value of
rms beam-width, rms width of correlation function, and size of aperture placed
at the Fourier plane of the lens system.
