Question

During an ATR experiment, what is the refractive index for when the penetration depth becomes infinite? What is happening at that point?

Answer 1

The Penetration Depth in ATR (Attenuated Total Reflection) experiment is inversly proportional to the refractive index of internal reflection element that is ATR crystal.

i.e. if the special kind of metamaterial is used with near 0 refractive index, the theoretical penetration depth approaches infinity.

The phase velocity of IR waves should be infinite for a zero-index material. Similarly, wavelength in a zero-index material should be infinite because it equals the wavelength in vacuum divided by refractive index.