THE RELATIONSHIP BETWEEN THE POYNTING VECTOR AND THE DISPERSION SURFACE IN THE BRAGG-CASE

The relationship between the Poynting vector and the dispersion surfac e in the symmetrical Bragg case is studied in detail. It is found that the Poynting vector is not normal to the real part of the dispersion surface in the so-called 'total reflection' region, even when the cont ribution of the imaginary part of the scattering factor to the diffrac tion is negligible. Unlike that in the Laue case, the deviation in the Bragg case becomes least when the diffraction is induced only by the imaginary part of the scattering part near the absorption edge.