Today 1/29  Lab Questions?  Air wedges, soap films, coatings  HW:1/29 “Air Wedge” handout Due Friday 1/31  Thursday:Begin Ch 26 Refraction  Peer guidance center (211 Wit) staffed: Mon - Thur, 1-4 Except Mon 2-3 and Tue 3-4 You are welcome to use room 211 anytime.

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest. Trough in Trough out Crest in Crest out Incoming wave Reflected wave

Thin Films Trough in Trough out Crest in Crest out Incoming wave Reflected wave Now invert the reflected wave (phase shift). This is like light bouncing off of a higher n material. No phase shift means that a trough bounces off a boundary as a trough and a crest bounces off a boundary as a crest.

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave Now invert the reflected wave (phase shift). This is like light bouncing off of a higher n material.

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Thin Films Phase shift means that a trough bounces off a boundary as a crest and a crest bounces off a boundary as a trough. Trough in Crest out Crest in Trough out Incoming wave Reflected wave

Antireflection coatings Setting up destructive interference for reflected light means that it all (mostly) is transmitted. Lens Coating Can’t do it for all wavelengths at once so choose green, in the middle of the visible spectrum. When n coating < n glass......both reflected rays phase shifted so 2t = (m + 1 / 2 ) coating gives destructive interference in the reflection. When n coating > n glass... …only one reflected ray is phase shifted so 2t = (m) coating gives destructive interference in the reflection.

Thin Films Eyeball The wavelength is different in the film. Wavelength ( ) Film thickness (PLD) Index of refraction (n) Phase shifts film = vacuum /n film

Thin Film Problems  Draw picture  Consider reflected wave phase shifts  none, one, or both can be shifted  Find in the film  Chose m or (m + 1 / 2 ) (use in the film)  Constructive or destructive?  Phase shifts?  PLD = 2t for thin films

Example: 665 nm light shines on a soap film nearly perpendicularly. The soap film has n = What is the minimum thickness of the film if this wavelength is strongly reflected? For air n = 1. One is phase shifted (front surface), the back surface reflection is not phase shifted. film = /n film = 665 nm /1.33 = 500 nm Want constructive but one is phase shifted so... we use (m + 1 / 2 ) film 2t = (m + 1 / 2 ) film minimum t when m = 0 2t min = ( 1 / 2 ) film t min = ( 1 / 4 ) film = 125 nm

Example: See example 11 Ch 27 Light shines on a soap film nearly perpendicularly. The film is 375 nm thick and has n = List the first four wavelengths of light for which constructive interference causes the film to look bright in reflected light. 2t = ? (m + 1 / 2 ) film since only one is phase shifted film air = n film film Visible light 1500 nm 500 nm 300 nm 214 nm 2000 nm 665 nm 399 nm 285 nm

Thin Films, Wedges Vertical soap film is thicker at the bottom. Pair of thick glass plates with a thin air wedge in between. The air is the thin film. Both will produce light and dark fringes because the thickness varies.

Thin Films, Wedges Soap film in reflected light. Thin at the top. 2t = 1 / 2 film 2t = 3 / 2 film 2t = 5 / 2 film 2t = 7 / 2 film 2t = 9 / 2 film 2t < 1 / 2 film t < 1 / 4 film !!! t = 1 / 4 film t = 3 / 4 film t = 5 / 4 film t = 7 / 4 film t = 9 / 4 film 2t = (m + 1 / 2 ) film for constructive since only one ray is phase shifted.

Thin Films, Wedges Air wedge in reflected light. Thin at the left. One is phase shifted and one is not so for constructive interference.... 2t = (m + 1 / 2 ) air It’s an “air” film Top view Where the glass touches, it will be dark. Why?

Thin Films, Wedges What about the transmitted light? No light reflected means all transmitted! Reflected Transmitted This is hard to observe This is easy to observe