1. See, for example: R.S. Chu, T. Tamir: Guided-wave theory of light diffraction by acoustic microwaves. IEEE Trans. MTT-18, 486?504 (1970), or
2. C. Elachi: Waves in active and passive periodic structures: A review. Proc. IEEE64, 666?1697 (1976)
3. L. Solymar, D.J. Cooke:Volume Holograms and Volume Gratings (Academic, New York 1981)
4. P.St.J. Russell: Phys. Rep.71, 209?312 (1981)
5. The process of tracing-back is actually more complicated than suggested in this simple discussion, although the basic idea is correct. The wavevector of then-th coupled-wave inside the grating is taken to be $$\bar k_n = \bar k_0 + nK$$ where $$\bar k_0$$ is the refracted wavevector of the incident wave, andK the grating vector. For each value ofn, a distinct coupled-wave is seen as existing inside the grating, and as giving rise to a discrete diffracted wave (possibly evanescent) outside the grating. Hence, one visualizes an external diffracted wave as arising from the coupled wave whose phase velocity parallel to the interface equals that of the external wave; the external wave is ?traced back? into that coupled wave