Effect of scattering on cross-spectral purity of light

The concept of cross-spectral purity was introduced by Mandel in connection with the modulation of spectral distribution of optical fields in superposition experiments. It is now known that spectral distribution of light can also change on scattering. We investigate the effect of scattering on cross-spectral purity. We show that the purity is, in general, not preserved on scattering. We also discuss some conditions under which it can be preserved at certain pairs of points in the far-zone.