Hint 8.7
Phase shifts only occur
On reflection, not on transmission
When light goes from a medium of lower index of refraction into a medium of higher index of refraction
If there are 0 or 2 phase shifts, the total path traveled must be an integral number of wavelengths (as measured in the thin film) for constructive interference to occur.
We can then generalize this result:
| Number of Phase Shifts |
Constructive Interference |
Destructive Interference |
| 0 or 2 |
2nt = mλ |
2nt = (m+½)λ |
| 1 |
2nt = (m+½)λ |
2nt = mλ |
Note that n is the index of refraction in the film, t
is the film thickness, and m = 0, 1, 2, ...
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