Integral method:
D. Maystre and E. Popov: “Integral method for
gratings,” in Gratings: Theory and Numeric Applications (Institut
Fresnel, PUP, 2012), Ch.4, 4.1-4.58 www.fresnel.fr/numerical-grating-book
E. Popov, B. Bozhkov, D. Maystre,
and J. Hoose: "Integral method for echelles covered with lossless or absorbing thin dielectric
layers," Appl. Opt. 38, 47-55 (1999) pdf