Thin Film

Thin Film#

Light of wavelength \(\lambda\_{\text{air}}\) = 611 nm is incident (from the air, \(n\_{air} = 1.00\)) on a thin film of unknown index of refraction and thickness. The film is attached to a glass surface (\(n\_{\text{glass}} = 1.5\)). The path length difference traveled by the light reflecting from the front and back surfaces of the film corresponds to \(\frac{\lambda\_{\text{film}}}{2}\) (half a wavelength). Light reflecting off both the front and back surfaces of the film experiences a \(\pi\) rad (initial) phase shift.

Part 1#

This implies that the reflected light from these two reflections will be;

Answer Section#

  • {‘value’: ‘in phase causing constructive interference of the reflected light. ‘}

  • {‘value’: ‘out of phase causing destructive interference of the reflected light. ‘}

Part 2#

What must the product of the film thickness and the film’s index of refraction be?

Answer Section#

Please enter in a numeric value in .

Part 3#

In order for both reflections to experience \(\pi\) rad phase shifts, what range of values can \(n\_{\text{film}}\) take?

Answer Section#

Please enter in a numeric value in .

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Answer Section#

Please enter in a numeric value in .

Part 4#

What is the lower limit on how thick the film could be, given your answers to on the previous questions?

Answer Section#

Please enter in a numeric value in .

Part 5#

If the thin film had a thickness of 148nm, what index of refraction would the thin film have to have?

Answer Section#

Please enter in a numeric value in .

Part 6#

If the film thickness was now doubled, the reflected light from the front and back surfaces of the film would be;

Answer Section#

  • {‘value’: ‘in phase causing constructive interference of the reflected light. ‘}

  • {‘value’: ‘out of phase causing destructive interference of the reflected light. ‘}

Part 7#

If you were to design anti-reflective coatings for glasses with this thin film material and this color of light, which film thickness would you choose?

Answer Section#

Please enter in a numeric value in .

Attribution#

Problem is licensed under the CC-BY-NC-SA 4.0 license.
The Creative Commons 4.0 license requiring attribution-BY, non-commercial-NC, and share-alike-SA license.