• Support PF! Buy your school textbooks, materials and every day products via PF Here!

Thin Film Reflection

  • Thread starter FizX
  • Start date
9
0
1. Homework Statement
A thin 1.00x10^-5 cm-thick film of MgF2 (n=1.38) is used to coat a camera lens. Are there any wavelengths in visible spectrum intensified in reflected light?


2. Homework Equations
thickness = wavelength/4n (n is refraction index)
?????


3. The Attempt at a Solution
I am guessing that the incoming light in the material reflects inside the material to cause constructive interference at certain wavelengths (which will be multiples of the thickness of the MgF2).
My main question is, how do I relate possible wavelengths to thickness of the material?
 

Andrew Mason

Science Advisor
Homework Helper
7,521
301
1. Homework Statement
A thin 1.00x10^-5 cm-thick film of MgF2 (n=1.38) is used to coat a camera lens. Are there any wavelengths in visible spectrum intensified in reflected light?


2. Homework Equations
thickness = wavelength/4n (n is refraction index)
?????


3. The Attempt at a Solution
I am guessing that the incoming light in the material reflects inside the material to cause constructive interference at certain wavelengths (which will be multiples of the thickness of the MgF2).
My main question is, how do I relate possible wavelengths to thickness of the material?
Reflection cannot add to the incident light intensity. What happens is that some frequencies are not reflected as intensely due to destructive interference within the wave coating so the frequencies which experience constructive interference appear to be more intense.

So the question is: at what frequency does the light reflected from the first surface (Air/MgF2) constructively interfere with light reflected from the second surface (MgF2/Glass).

The reflections at both surfaces undergo a phase change of 180 so these phase shifts cancel out. In order to have constructive interference, what must the path from surface 1 to 2 and back to 1 represent in terms of wavelength of the light in the MgF2 medium?

Work out the frequency of the light from the wavelength.

AM
 

Related Threads for: Thin Film Reflection

Replies
3
Views
4K
Replies
3
Views
14K
  • Posted
Replies
1
Views
185
Replies
1
Views
901
Replies
1
Views
516
Replies
6
Views
428
Replies
6
Views
739

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top