Interference Flashcards
what happens when 2 waves of the same wavelength combine
what happens when 2 waves out of step add up
add up, yielding a wave twice the amplitude
cancel each other out
what is the most important optometric application of interence
anti-reflective coating placed on both surfaces of the lens to reduce reflections
what are modern A/R coatings
mulit-layer for maximum suppression of reflections
what is a design wavelength
a single layer coating is maximally effective only at one wavelenth
what is a wavefront
surface of constant phase
-imagine a point source emitting light waves that travel in all directions
how does a wavefront from a point source look
spherical
as we get farther from source and look at a small area of the sphere then the wavefront is essentially planar
how can a plane wavefront be created
by putting the light through a collimating lens
when will the next bright band occur in young’s double slit after the midline
where the path difference btwn the rays is a whole wavelength
where are the dark bands located in regards to the bright band to youngs double slit
dark bands always midway btwn bright bands
why does a thin layer of any material have the capability of producing interference
bc it divides incidnet light into multiple reflected and transmitted rays
will better cancellation result from reflected or transmitted rays
reflected rays
where are observations made in interfernece in a wedge
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
where is interference observed in a wedge
btwn the rays that are refelcted back form the surfaces that form the wedge
at the line where the 2 plates are in contact the path difference is ____ but there is a dark band ther ebc…
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
why are the dark bands straight lines in an air wege
bc the plates are flat and the path diff btwn the rays is the same all the way across the plates
in newtons rings, the central spot is dark and the first bright ring is white, why
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
why are soap bubbles diff colors randomly
how do anti-reflective coatings work
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
how does A/R layer thickness work
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
why must the thickness of the A/R layer be 1/4 wavelength
bc one ray makes 2 trips through the A/R layer
