Talk:Total refraction

I think that the negative refractive index is not a requirement. Optical impedance is defined as

$$Z=\sqrt{\varepsilon/\mu}$$.

For total refraction impedances must match, i.e. $$Z_1=Z_2$$. If $$\epsilon_1=-\epsilon_2$$ and $$\mu_1=-\mu_2$$ then this condition is certainly fulfilled, but it is, obviously, not the only possible pair of numbers that satisfy the equation

$$\frac{\varepsilon_1}{\mu_1}=\frac{\varepsilon_2}{\mu_2}$$