Standing waves and reflectivity from ultrathin layer

We have analytically found that the reflectivity amplitude from one thin layer in the presence of the other reflecting layers is modulated by the squared amplitude of the radiation field but not by the first order amplitude as it was supposed in the paper of R. Röhlsberger (Hyperfine Interactions 123/124, 455 (1999)) for the delayed nuclear resonance reflectivity. Hence, a larger sensitivity to the standing waves is expected for the reflectivity signal from selected groups of atoms or nuclei compared with the secondary radiation emission.