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Flashcards in Interference Deck (20)
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1
Q

what happens when 2 waves of the same wavelength combine

what happens when 2 waves out of step add up

A

add up, yielding a wave twice the amplitude

cancel each other out

2
Q

what is the most important optometric application of interence

A

anti-reflective coating placed on both surfaces of the lens to reduce reflections

3
Q

what are modern A/R coatings

A

mulit-layer for maximum suppression of reflections

4
Q

what is a design wavelength

A

a single layer coating is maximally effective only at one wavelenth

5
Q

what is a wavefront

A

surface of constant phase

-imagine a point source emitting light waves that travel in all directions

6
Q

how does a wavefront from a point source look

A

spherical

as we get farther from source and look at a small area of the sphere then the wavefront is essentially planar

7
Q

how can a plane wavefront be created

A

by putting the light through a collimating lens

8
Q

when will the next bright band occur in young’s double slit after the midline

A

where the path difference btwn the rays is a whole wavelength

9
Q

where are the dark bands located in regards to the bright band to youngs double slit

A

dark bands always midway btwn bright bands

10
Q

why does a thin layer of any material have the capability of producing interference

A

bc it divides incidnet light into multiple reflected and transmitted rays

11
Q

will better cancellation result from reflected or transmitted rays

A

reflected rays

12
Q

where are observations made in interfernece in a wedge

A

in reflected light bc to obtain good cancellation for destructive interference the 2 waves have to have nearly equal amplitudes
-easier when bands are very dark

13
Q

where is interference observed in a wedge

A

btwn the rays that are refelcted back form the surfaces that form the wedge

14
Q

at the line where the 2 plates are in contact the path difference is ____ but there is a dark band ther ebc…

A

zero

bc one of the rays undergo a 1/2 wavelength phase shift and the other does not, putting them out of phase=dark band

15
Q

why are the dark bands straight lines in an air wege

A

bc the plates are flat and the path diff btwn the rays is the same all the way across the plates

16
Q

in newtons rings, the central spot is dark and the first bright ring is white, why

A

bc the small path diff brings most of the wavelenths into register at the same time -after that diff wavelengths are in constructive interference at diff places resulting in a sequence of colored rings

17
Q

why are soap bubbles diff colors randomly

A
18
Q

how do anti-reflective coatings work

A

reflections are suppressed by adding a thin transparent layer to the lens surfaces, causing destructive interference btwn the light rays reflected from the 2 surfcaes of this thin layer

19
Q

how does A/R layer thickness work

A

the thickness must be such that the rays reflected from the 2 side of the anti-reflective layer are 1/2 wavelength out of phase

20
Q

why must the thickness of the A/R layer be 1/4 wavelength

A

bc one ray makes 2 trips through the A/R layer