Light Interference and Interferometry Overview
Interference and
Interferometry
By R Seguin
What is light interference?
•
Remember sound interference?
•
Its like that but with light. Simple as that.
•
the Path Length Difference equals some number multiplied
by the wavelength and we have different levels of
interference depending on what that number is PLD = m
λ
•
When two waves of light converge they can cause the light
we see to change just like how sound interference changes
the sound we hear
•
Its often caused by diffraction
Examples of interference
•
Young’s double slit experiment
•
Supernumerary rainbows
•
Thin film interference
Double slit experiment
•
The double slit experiment is a
very classic way to view
interference of light
•
But is easier to do in theory than
experimentally since the distance
between the slits has to be very
small and so do the slits
themselves, there is only
interference if they openings are
about the width of the
wavelength or less
Those other things I mentioned
Supernumerary rainbows are the lighter rainbows inside
the main rainbow created by the interference of the
light diffracting after coming out of very small water
dropets
Thin film interference is formed by some of the light
reflecting off of the top of the film while other light
reflects off the surface under the film thus creating
a difference in the distance traveled by the two
waves putting them out of phase.
Math
Double slit formula: dsin
θ
= m
λ
this only holds if d and a are both
very small distance and D is much much larger than both
Thin film: 2n
2
dcosθ
2
= m
λ
using Snell's law we can
use n
1
sin(θ
1
) = n
2
sin(θ
2
) to find θ
2
general rule: PLD = m
λ we have complete constructive interference when m = n = {0,1,2,3…} we will haveperfect destructive interference when m = n + 0.5
What is interferometry?
•
Interferometry is a general term for
sciences that use the interference of
electromagnetic waves to collect data.
•
Interferometry is quite wide reaching
with uses in fields from astronomy to
medicine.
•
Because the maximum interference
values happen every time the path
length difference is half a wavelength
and the wavelength of light is very small
we can make very precise readings but
these devices are easily disturbed by any
nearby vibrations.
Very basic diagram of an interferometer
history
Measurement of the speed of light
One of the mirrors on an interferometer is fixed the other we can
move. So we adjust that mirror until we have either complete
constructive interference or complete destructive interference.
The difference between the distance traveled by the two rays of light is
our PLD and so based on when we get complete constructive
interference the distance between the placements of the mirror is our
wavelength, and so is we know the frequency of the light we are using
we get the speed.
Δd =
λ
c =
λ
f
Gravitational waves
First hypothesized by Albert Einstein (although we don’t know how much
work was done by his first wife Mileva Maric) in 1916 in the general theory
of relativity. Essentially they are ripples in space-time created by dramatic
changes in how an object is affecting space-time like a supernova collapsing
into a black hole or a massive object with a huge acceleration moving
towards another massive object. These waves are some of the weakest
forces in the universe needing one of the most sensitive of measuring
devices ever created to observe even the most powerful of GWs
Laser Interferometer Gravitational-Wave
Observatory
The observatory consists of two massive
interferometers. One located in Hanford Washington
and one in Livingston Louisiana. The reason they are
so far apart is so local vibrations can be ruled out
while looking for the same interference at the same
time from both locations, then that data is sent to
other observatories to see if they got similar results.
Each arm of these interferometers are 4km long
On September 14 2015 LIGO observed actual
physical affects of gravitational waves for the first
time
Thee waves were caused by two black holes
colliding but by the time they reached earth they
only moved space-time an less than the diameter of
a proton.
Holographic interferometry
This type of interferometry involves the superposition of holograms of
a object that is being studied.
Any movement of the object causes interference
this movement can be caused by vibration, heating, stress, etc.…
analyzing this interference can give information about the object
Sample test question
Light of wavelength 510nm is traveling at a thin film of oil on top of water at an
angle of 60° above the horizontal. the refractive index of air is 1.00 and the index of
oil is 1.46. what is the first thicknesses d of the film of oil for which we would have
complete destructive interference?
Answer: about 93nm
Is this realistic? Well the
approximate thickness of one
molecule of olive oil is 2nm and
oil can spread out to be a
molecule thick on a large enough
water surface, so yes it is.
Bibliography
"Double Slit Interference."
Slit Interference
. Hyperphysics, n.d. Web. 30 May 2017.
<http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/slits.html>.
Hariharan, P.
Basics of Interferometry
. Amsterdam: Elsevier, 2007. Print.
"History of Interferometers." N.p., n.d. Web. 6 June 2017. <http://ffden-
2.phys.uaf.edu/212_fall2003.web.dir/Rahnia_Parker/history.htm>.
"holographic interferometry."
The Penguin Dictionary of Physics
, edited by John Cullerne,
Penguin, 4th edition, 2009.
Credo Reference
,
http://www.student.wvc.edu:2548/content/entry/pendphys/holographic_interferometry/0. Accessed 30
May 2017.
"Learn More."
LIGO Lab
. Caltech and MIT, n.d. Web. 30 May 2017.
<https://www.ligo.caltech.edu/page/learn-more>.
"Oil Film Interference."
Thin Film Reflection and Interference
. Hyperphysics, n.d. Web. 30 May
2017. <http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/oilfilm.html>.
Serway, Raymond, and John Jewett. "Interference of Light Waves."
Physics for Scientists and
Engineers
. 7th ed. N.p.: Cengage Learning, 2007. 1051-099. Print.
Wolf, Emil, and Max Born.
Principles of Optics: Electromagnetic Theory of Propagation,
Interference and Diffraction of Light
. Oxford: Pergamon, 1970. Print.
Young's Double Slit Introduction
. Dir. David SantoPietro.
Khan Acadeny
. Youtube, 07 July 2014.
Web. 29 May 2017. <https://www.khanacademy.org/science/physics/light-waves/interference-of-light-
waves/v/youngs-double-split-part-1>.
Light interference occurs when two waves of light converge, causing changes in what we see, similar to sound interference. Examples include double slit experiments and supernumerary rainbows. Interferometry, a scientific technique utilizing electromagnetic wave interference, is a widely used method for data collection.
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Presentation Transcript
Interference and Interferometry By R Seguin
What is light interference? Remember sound interference? Its like that but with light. Simple as that. the Path Length Difference equals some number multiplied by the wavelength and we have different levels of interference depending on what that number is PLD = m When two waves of light converge they can cause the light we see to change just like how sound interference changes the sound we hear Its often caused by diffraction
Examples of interference Young s double slit experiment Supernumerary rainbows Thin film interference
Double slit experiment The double slit experiment is a very classic way to view interference of light But is easier to do in theory than experimentally since the distance between the slits has to be very small and so do the slits themselves, there is only interference if they openings are about the width of the wavelength or less
Those other things I mentioned Supernumerary rainbows are the lighter rainbows inside the main rainbow created by the interference of the light diffracting after coming out of very small water dropets Thin film interference is formed by some of the light reflecting off of the top of the film while other light reflects off the surface under the film thus creating a difference in the distance traveled by the two waves putting them out of phase.
general rule: PLD = mwe have complete constructive interference when m = n = {0,1,2,3} we will have perfect destructive interference when m = n + 0.5 Math Thin film: 2n2dcos 2 = m using Snell's law we can use n1sin( 1) = n2sin( 2) to find 2 Double slit formula: dsin = m this only holds if d and a are both very small distance and D is much much larger than both
What is interferometry? Interferometry is a general term for sciences that use the interference of electromagnetic waves to collect data. Interferometry is quite wide reaching with uses in fields from astronomy to medicine. Because the maximum interference values happen every time the path length difference is half a wavelength and the wavelength of light is very small we can make very precise readings but these devices are easily disturbed by any nearby vibrations. Very basic diagram of an interferometer
history The first interferometer was created by Albert Michelson, him and his colleague Dr. Edward Morley wanted to use it to prove the existence of the luminiferous ether they kept creating more and more sensitive devices but nothing changed thus, by accident, disproving the ether s existence In 1958 K.D. Froome used radio waves(radio waves are light with frequency from 104 to 1012) of a set frequency in an interferometer and used that to measure the speed of light The invention of the laser made interferometers able to be even more accurate since we can now have focused beams of light at a much wider range of frequencies thus giving us longer or shorter wavelengths depending on the need In 1972 Evenson Et Al made an even more accurate measurement of the speed of light using a laser interferometer
Measurement of the speed of light One of the mirrors on an interferometer is fixed the other we can move. So we adjust that mirror until we have either complete constructive interference or complete destructive interference. The difference between the distance traveled by the two rays of light is our PLD and so based on when we get complete constructive interference the distance between the placements of the mirror is our wavelength, and so is we know the frequency of the light we are using we get the speed. d = c = f
Gravitational waves First hypothesized by Albert Einstein (although we don t know how much work was done by his first wife Mileva Maric) in 1916 in the general theory of relativity. Essentially they are ripples in space-time created by dramatic changes in how an object is affecting space-time like a supernova collapsing into a black hole or a massive object with a huge acceleration moving towards another massive object. These waves are some of the weakest forces in the universe needing one of the most sensitive of measuring devices ever created to observe even the most powerful of GWs
Laser Interferometer Gravitational-Wave Observatory The observatory consists of two massive interferometers. One located in Hanford Washington and one in Livingston Louisiana. The reason they are so far apart is so local vibrations can be ruled out while looking for the same interference at the same time from both locations, then that data is sent to other observatories to see if they got similar results. Each arm of these interferometers are 4km long On September 14 2015 LIGO observed actual physical affects of gravitational waves for the first time Thee waves were caused by two black holes colliding but by the time they reached earth they only moved space-time an less than the diameter of a proton.
Holographic interferometry This type of interferometry involves the superposition of holograms of a object that is being studied. Any movement of the object causes interference this movement can be caused by vibration, heating, stress, etc. analyzing this interference can give information about the object
Sample test question Light of wavelength 510nm is traveling at a thin film of oil on top of water at an angle of 60 above the horizontal. the refractive index of air is 1.00 and the index of oil is 1.46. what is the first thicknesses d of the film of oil for which we would have complete destructive interference? Answer: about 93nm Is this realistic? Well the approximate thickness of one molecule of olive oil is 2nm and oil can spread out to be a molecule thick on a large enough water surface, so yes it is.
Bibliography "Double Slit Interference." Slit Interference. Hyperphysics, n.d. Web. 30 May 2017. <http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/slits.html>. Hariharan, P. Basics of Interferometry. Amsterdam: Elsevier, 2007. Print. "History of Interferometers." N.p., n.d. Web. 6 June 2017. <http://ffden- 2.phys.uaf.edu/212_fall2003.web.dir/Rahnia_Parker/history.htm>. "holographic interferometry." The Penguin Dictionary of Physics, edited by John Cullerne, Penguin, 4th edition, 2009. Credo Reference, http://www.student.wvc.edu:2548/content/entry/pendphys/holographic_interferometry/0. Accessed 30 May 2017. "Learn More." LIGO Lab. Caltech and MIT, n.d. Web. 30 May 2017. <https://www.ligo.caltech.edu/page/learn-more>. "Oil Film Interference." Thin Film Reflection and Interference. Hyperphysics, n.d. Web. 30 May 2017. <http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/oilfilm.html>. Serway, Raymond, and John Jewett. "Interference of Light Waves." Physics for Scientists and Engineers. 7th ed. N.p.: Cengage Learning, 2007. 1051-099. Print. Wolf, Emil, and Max Born. Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light. Oxford: Pergamon, 1970. Print. Young's Double Slit Introduction. Dir. David SantoPietro. Khan Acadeny. Youtube, 07 July 2014. Web. 29 May 2017. <https://www.khanacademy.org/science/physics/light-waves/interference-of-light- waves/v/youngs-double-split-part-1>.
