No office hours tomorrow  I also procrastinate . . .

Why don’t I see an interference pattern From two light bulbs?

Coherence (temporal and spatial) Polarization

Interference of BEC

4 4 Phase Shift on Reflection of Light 2 1.0

0.5

2 4 Low

n

to high

n

180 degree phase shift 0.5

1.0

1.0

0.5

2 2 4 High

n

to low

n

no phase shift 0.5

1.0

A soap film in air is illuminated with light near normal incidence (angles exaggerated).

n=1 n=1.3

n=1

A soap bubble has an index of n=1.3. A series of colorful fringes are seen in the reflection from the lower part of the soap film where it has gradually greater thickness. What is the minimum thickness of the film that will produce a bright green fringe (λ=530nm) when looking from above?

We see thin film interference all the time. Why no thick film intereference?

A.

B.

C.

D.

E.

Group problem: What is the minimum thickness of a glycerin film (n=1.47) on which light of wavelength 600 nm shines that results in constructive interference of the reflected light? Assume the film is surrounded front and back by air.

72 nm 102 nm 150 nm 204 nm 300 nm

Discussion question: An oil film on water reflects different colors more or less brightly owing to interference, depending on the film thickness. All the colors reflect brightly when the film is really thin (i.e., for films much smaller than visible wavelengths, white light reflects relatively well). From this information, we can tell that the index of refraction of the oil is A.

B.

C.

Less than that of water.

The same as that of water.

Greater than that of water.

The two reflected rays must be in-phase with each other when they reflect because the second one does not travel significantly further than the other.

The n of oil is higher than air so there is a phase shift of 180.

Therefore the n of water must also cause a phase shift so n oil < n water

 A soap bubble has an index of n=1.3. The bubble is thinnest near the top, and there is no reflection from that region where it is very thin. A series of colorful fringes are seen in the reflection from the lower part of the soap film where it has gradually greater thickness. How thick is the film at the first bright green fringe (λ=530nm) near the top?

 A soap film has an index of n=1.3. The bubble is thinnest near the top, and there is reflection from that region where it is very thin. A series of colorful fringes are seen in the reflection from the lower part of the soap film where it has gradually greater thickness. How thick is the film at the first bright green fringe (λ=530nm) near the top?

MOSIAH 18:8 And it came to pass that he said unto them: Behold, here are the waters of Mormon (for thus were they called) and now, as ye are desirous to come into the fold of God, and to be called his people, and are willing to bear one another’s burdens, that they may be light;

Practical Uses of Interference  Active Sound Control  Nature uses it . . .

http://www.youtube.com/watch ?v=jeUd_ittNns

Practical Uses of Interference  Active Sound Control  Nature uses it . . .

 Anti-reflective coatings on lenses

Practical Uses of Interference  Active Sound Control  Nature uses it . . .

 Anti-reflective coatings on lenses  Extremely reflective mirrors  Selectively reflective mirrors  Interferometry

Michelson Interferometer

Michelson Interferometer

Michelson Interferometer

How much do I need to move a mirror?

f 1 p /2 Cesium Interferometer f 2 f 3 p /2 1 p 0 -1 -10 -5 0 5 10 Rotation rate (x10 -5 ) rad/sec 15 20

Ion Interferometer