In searching for justification of the "universality" of the above (law and angle), I discovered the std. text. **, when I was a student, justifies the law as experimentally "proved". My favo. reference text** uses Huygens' construction.
Anyway, I'm satisfied Snell's law and its corollaries are valid for N < 1.
Any comment before I use in my discussion of my waveguide prism and lens?
** Jenkins and white; Eisberg and Lerner
bc assumes Huygens is justified by Maxwell.
p.s. when N < 1 is substituted in the formula for prism min. deviation, the deviation is negative, as expected. BTW, I couldn't solve the eq.** for the deviation, and didn't find by googling -- anyone know?