A diamond surface is patterned with a moth-eye antireflection grating of period
PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Wave propagation and light in media · Interference and diffraction
What an Instrument Can See, Ch Media that are designed: plasmons, metamaterials and photonic crystals
Problem
A diamond surface is patterned with a moth-eye antireflection grating of period Λ=150nm, exactly as the silicon moth-eye of section 7.3, with a mean index inside the graded layer of nˉ=2.4 used for the averaging test.
((a)) Decide, using the criterion of section 7.3 (Λ against λ/2nˉ), whether the coating acts as an effective medium or instead behaves as a genuine periodic structure at a vacuum wavelength of 900nm, and again at 450nm.
((b)) For whichever of the two wavelengths fails that test, compare Λ with the vacuum wavelength, as section 7.3 did for the silicon moth-eye. Decide whether the coating still suppresses reflection back into the air at that wavelength, and say in one sentence what the periodicity can now do inside the diamond that a true effective medium would not do.