Question

A camera lens in air (index 1.00) is coated with a thin film with a thickness L that maximizes the transmitted light (and minimizes the reflected light) for a particular wavelength. If the thin film has an index of 1.25 and the lens material an index of 1.50, what minimum thickness L is required? (Let λn be the wavelength in the thin film.)

Answer 1

t = 100 nm

Step-by-step explanation:

given,

Refractive index of coating is n ' = 1.25

refractive index of glass is n = 1.5

assuming wavelength of the film = 500 nm

destructive interference is

`m +(1)/(2)* \lambda = 2 n't`

`t = (m +(1)/(2)* \lambda )/(2 n')`

for minimum thickness m = 0

`t = (0+(1)/(2)* \lambda)/(2 n')`

`t = (500)/(4 n')`

`t = (500)/(4* 1.25)`

t = 100 nm

hence, the minimum thickness required is t = 100 nm