Redshift and blueshift in the spectra of lights coherently and diffusely scattered from random rough interfaces

We show theoretically and experimentally that the spectrum of coherently scattered light from a randomly rough interface in reflection and transmission is redshifted with a shrinkage in spectral width. In reflection mode the amounts of the redshift and the shrinkage depend on interface roughness, incident angle, and the spectral width of the illuminating light. In transmission mode they also depend on the refractive indices of the surrounding media. The redshift and width shrinkage increase with decrease of the coherently scattered light intensity. This study shows that the spectrum of the diffusely scattered light is blueshifted in the specular direction and in directions with small scattering angles only in situations with appreciable intensity of the coherently scattered light. With decrease of the latter intensity the blueshift reduces and turns into redshift. Also, the redshift and blueshift decay with increase of the scattering angle. An experimental investigation has been carried out, on sheet glasses with different roughness on one side, in reflection and transmission modes. The experimental results and theoretical predictions are quite consistent.