Final answer:
Destructive interference in thin film coatings, like anti-reflective lenses, occurs when the path length difference is a half-integral wavelength, leading to minimized light reflection at specific wavelengths.
Step-by-step explanation:
The concept discussed here relates to destructive interference in thin film equations used for anti-reflecting coatings. When light waves reflect off the surfaces of a film, they can interfere with each other, leading to either constructive or destructive interference. For destructive interference to occur in a thin film like an anti-reflective coating, the path length difference between the two waves should be a half-integral multiple of the light's wavelength. This phenomenon is employed in various applications such as reducing glare in sunglasses or improving the image clarity in camera lenses via non-reflective coatings.
To achieve destructive interference, the thinnest possible layer of material—such as magnesium fluoride with an index of refraction of 1.38 used on camera lenses—is applied to minimize reflections of a specific wavelength of light. For example, to limit the reflection of 550-nm light (the most intense visible wavelength), you need to calculate the optimal thickness based on the refractive indices of the coating and the material beneath it.