Sophisticated cameras use a series of several lenses. Light can reflect from the surfaces of these various lenses and degrade image clarity. To limit these reflections, lenses are coated with a thin layer of magnesium fluoride that causes destructive thin film interference. What is the thinnest this film can be, if its index of refraction is 1.38 and it is designed to limit the reflection of 550-nm light, normally the most intense visible wavelength? The index of refraction of glass is 1.52.

Strategy

Refer to Figure 27.33 and use n₁ = 1.00 for air, n₂ = 1.38, and n₃ = 1.52. Both ray 1 and ray 2 will have a λ/2 shift upon reflection. Thus, to obtain destructive interference, ray 2 will need to travel a half wavelength farther than ray 1. For rays incident perpendicularly, the path length difference is 2t.

Data from figure 27.33

Transcribed Image Text:

Incident light n₁ n₂ n3 1 2