A film is coated on the surface of a lens to maximize transmission at λ = 660 nm. If the index of refraction of the film is 1.3 (which is lower than the index of refraction of the glass), what is the thickness of the film (in nm) ? Hint: maximum transmission occurs when reflection is at a minimum.

Question

Physics

Iris Gillespie

4 March, 10:37

A film is coated on the surface of a lens to maximize transmission at λ = 660 nm. If the index of refraction of the film is 1.3 (which is lower than the index of refraction of the glass), what is the thickness of the film (in nm) ? Hint: maximum transmission occurs when reflection is at a minimum.

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Brennan Huerta · Answer 1

Transmission is maximum when reflection is minimum.

Reflection is minimum when

Path difference is integral multiple of wavelength or

2μd = n λ or integral multiple of it (d is thickness of film)

minimum d = λ / 2μ = 660 nm / 2 x 1.3 = 253.85 nm.

Thickness may be 253.85 nm or its integral multiple.