Condition for far-zone spectral isotropy of light transmitted from Young's pinholes scattering on a quasi-homogeneous medium

The far-zone spectral isotropy of light transmitted from Young's pinholes on scattering from a quasi-homogeneous medium has been discussed. A sufficient condition for the far-zone spectral isotropy has been derived as a new scaling law. Our result not only is analogous with the scaling law for weak scattering in previous works but is also applicable for a more general situation where the incident light has an arbitrary spectral degree of coherence. More discussion about cross-spectral purity of the far field is presented.