1. Air-Water (n=1.3)-Air film (soap film) Normal incidence
Can we make a device with greater contrast in transmission? T
Dd/l

2. Air-Diamond (n=2.4)-Air filmT
F = 0.88
Dd/l

3. Air- Kryptonite? (n=10) -Air
F = 18
Dd/l
Interference ideas for why increasing r makes these peaks so sharp?

4. Multiple reflection view of T at low angle
As long as |x| < 1, this will converge
But for |x| 1, the dependence on phase is very fast!

5. If |r|,|r’| approach 1, many reflections contribute to the interference for R and T. Many phasors of nearly equal size give much more contrast in magnitude and much sharper features than just a few of very different size.
Very important concept in many contexts of interference

6. Multiple reflection view of T
Suppose R = rr = The relative strength of the first three transmitted fields are 1, 0.1, 0.01… etc .
If added in phase (0 shift) you get ____
If added out of phase (p shift) , you get ____
Max/min fields______ Max/min T’s _______

7. Multiple reflection view of T
Suppose R = rr = The relative strengths of the transmitted fields are 1, 0.75, …. etc . Now we must add many more fields to get the transmission.

8. Multiple reflection view of T
Sketch with phasors the addition of the fields 1, 0.75, …. etc in phase
This adds up to something close to 2 4 6 8 10

9. Multiple reflection view of T
Sketch with phasors the addition of the fields 1, 0.75, …. Out of phase (p shift)
This adds up to something close to
0.1
0.2
0.4
0.6 1
Max/min fields______ Max/min T’s _______

10. Multiple reflection view of T
Sketch with phasors the addition of the fields 1, 0.75, …. at p/4 shift
This adds up to something close to
0.2
0.4
0.6 1 2
Do the same for 1, 0.1, 0.01
In a relative sense, which is most sensitive to phase?

11. General feature of wave interference: if you want sharp features you have to add lots of waves with varying phase. (e.g. Fourier)

12. If I want to make an instrument that distinguishes wavelengths, I can get sharp transmission by increasing n to increasing R.
But it’s hard to obtain and work with kryptonite.

13. Fabry-Perot Etalon/Interferometer
High R due to large k in in metal coating.

14. Fabry-Perot Etalon/interferometer for low R:
Fabry-Perot Etalon/interferometer for high R, same d
Red: l = 1.00
Blue: l = 1.01
Is the device most sensitive to l changes for small or large d?

15. Free spectral range:
At a given d, how much can l change before it confuses us by “lapping” its original peak near d?

16. Given a choice, is it better to increase d or increase R to make as small as possible?
a) increase d
b) increase R

17. Multiple reflection view of T

18. Solar corona taken with the LASCO C1 coronagraph which employed a tunable Fabry-Pérot interferometer near an iron atom emission line at nm. Color coded image of the doppler shift of the line, after subtracting solar rotation.

19. What you see on a screen for any interferometer
There is always some angular divergence

20. Two close sodium emission lines are visible
Experiment on video