1. G. Toraldo di Francia:Nuovo Cimento,16, 61 (1960).
2. The mean velocity of energy transport (MVET), defined as the ratio of the time average of the Poynting vector to that of the energy density, has been introduced by Sommerfeld and Brillouin in their famous work on electromagnetic wave propagation in the region of anomalous dispersion (see for example W. K. H. Panofsky and M. Phillips:Classical Electricity and Magnetism, Second Edition (Reading, Mass., 1962), p. 413). The fact that for a circularly polarized evanescent wave the MVET reachesc, has been given independently by J. Ricard(Compt. Rend.,270, 381 B (1970)) and by J. L. Agudín (ICTP, Trieste, Int. Rep. IC/70/64 andPhys. Lett.,35 A, 107 (1971)).
3. J. L. Agudín, A. M. Platzeck andJ. R. Albano:Phys. Lett.,65 A, 77 (1978).
4. J. L. Agudín andA. M. Platzeck:On the limit for ß → 0 of the Toraldo di Francia expansion, Lett. Nuovo Cimento,22, 13 (1978).
5. The fact that a circularly polarized electromagnetichomogeneous plane wave carries angular momentum (which results proportional to its energy), stems from the model discussed, among others, byR. Feynman (The Feynman Lectures on Physics, Vol.3, Chap. 17 (Reading, Mass., 1965), p. 10) and by B. Rossi(Optics (Reading, Mass., 1957), p. 411). In ref. (3) it has been tacitly assumed that this model remains valid for circularly polarizedevanescent waves.