Optical Holography

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Optical Holography
PHYS 3232 Optics Fall 2008

• Ajeya Karajgikar
• Georgia Institute of Technology

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Topics covered

• What is holography?
• History of holography Timeline
• Basic terms and concepts in holography
• Interference
• Fresnel Zone Lens
• Visibility
• Influence of polarization
• Holographic recording and reconstruction
• Fundamental Imaging Techniques in Holography
• Formation of holograms in general
• Basic holography equations
• Holography in everyday life
• Interesting articles to read on holography

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What is holography?

• Holography is a technique that allows the light
  scattered from an object to be recorded and later
  reconstructed so that it appears as if the object
  is in the same position relative to the recording
  medium as it was when recorded. The image changes
  as the position and orientation of the viewing
  system changes in exactly the same way as if the
  object was still present, thus making the
  recorded image (hologram) appear three
  dimensional. Holograms can also be made using
  other types of waves.
• The technique of holography can also be used to
  optically store, retrieve, and process
  information. While holography is commonly used to
  display static 3-D pictures, it is not yet
  possible to generate arbitrary scenes by a
  holographic volumetric display.

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History of Holography

• Holography was invented in 1947 by Hungarian
  physicist Dennis Gabor (19001979), work for
  which he received the Nobel Prize in Physics in
  1971.

Gabor's research focused on electron optics,
which led him to the invention of holography. The
basic idea was that for perfect optical imaging,
the total of all the information has to be used
not only the amplitude, as in usual optical
imaging, but also the phase. In this manner a
complete holo-spatial picture can be obtained.
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History of Holography - Timeline

• Dennis Gabor, inventor of holography, stands
  beside his 18"x24" laser transmission, pulsed
  portrait. The historic portrait was recorded in
  1971 by R. Rinehart, McDonnell Douglas
  Electronics Company, St. Charles, MO to
  commemorate Gabor's winning of the Nobel Prize
  that year.

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History of Holography - Timeline
Dr. Dennis Gabor signs a copy of the Museum of
Holography's inaugural exhibition catalogue,
"Through The Looking Glass," during his historic
visit to the museum on March 17, 1977. (Photo by
Paul D. Barefoot)
At the time Gabor developed holography, coherent
light sources were not available, so the theory
had to wait more than a decade until its first
practical applications were realized, though he
experimented with a heavily filtered mercury arc
light source. The invention in 1960 of the laser,
the first coherent light source, was followed by
the first hologram, in 1963, after which
holography became commercially available.
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History of Holography Timeline (1962)
"Train and Bird" is the first hologram ever made
with a laser using the off-axis technique. This
pioneer image was produced in 1964 by Emmett
Leith and Juris Upatnieks at the University of
Michigan only four years after the invention of
the laser
In 1962 Emmett Leith and Juris Upatnieks of the
University of Michigan recognized from their work
in side-reading radar that holography could be
used as a 3-D visual medium. In 1962 they read
Gabor's paper and "simply out of curiosity"
decided to duplicate Gabor's technique using the
laser and an "off-axis" technique borrowed from
their work in the development of side-reading
radar. The result was the first laser
transmission hologram of 3-D objects (a toy train
and bird). These transmission holograms produced
images with clarity and realistic depth but
required laser light to view the holographic
image.
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History of Holography Timeline (1962)

• Leith and Upatnieks preparing to shoot a laser
  transmission hologram using the "off-axis"
  technique borrowed from their work in the
  development of side-reading radar. (Photo by
  Fritz Goro for Life Magazine, 1967)

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History of Holography Timeline (1962)
Russian scientist Yuri N. Denisyuk, State Optical
Institute in Leningrad, USSR, signing a copy of
his book, Fundamentals of Holography. (Photo by
Dr. Stephen Benton, 1979)

• Dr. Yuri N. Denisyuk of the U.S.S.R. combined
  holography with 1908 Nobel Laureate Gabriel
  Lippmann's work in natural color photography.
  Denisyuk's approach produced a white-light
  reflection hologram which, for the first time,
  could be viewed in light from an ordinary
  incandescent light bulb.

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History of Holography Timeline (1967)

• The 1967 World Book Encyclopedia Science Yearbook
  contained what is arguably the first
  mass-distributed hologram, a 4"x3" transmission
  view of chess pieces on a board. An article
  describing the production of the hologram and
  basic information about the history of holography
  accompanied it. A .05 watt He-Ne laser was used
  on a nine-ton granite table in a 30-second
  exposure to make the original from which all the
  copies were produced.

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History of Holography Timeline (1967)

• Also in 1967, Larry Siebert of the Conductron
  Corporation used a pulsed laser that he designed
  to make the first hologram of a person. The
  Conductron Corporation (later acquired by
  McDonnell Douglas Electronics Corporation) played
  an important role in the early days of commercial
  display holography. Their mass production and
  large plate capabilities serviced a tentative but
  potentially large market. Their gang-printed
  reflection holograms provided burgeoning
  marketing organizations with an exciting new
  promotional tool. Their large 18 x 24 inch plates
  made unusual trade show displays. The trend
  continued for several years until the recession
  in the early 1970s forced the company to close
  the pulsed laser facility.

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History of Holography Timeline (1968)
Dr. Stephen A. Benton, Massachusetts Institute of
Technology, seen through "Crystal Beginning," a
white light transmission hologram produced at the
Polaroid Corporation in 1977.(Photo by Michael
Lutch for WGBH, Boston)

• A major advance in display holography occurred in
  1968 when Dr. Stephen A. Benton invented
  white-light transmission holography while
  researching holographic television at Polaroid
  Research Laboratories. This type of hologram can
  be viewed in ordinary white light creating a
  "rainbow" image from the seven colors which make
  up white light. The depth and brilliance of the
  image and its rainbow spectrum soon attracted
  artists who adapted this technique to their work
  and brought holography further into public
  awareness.

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History of Holography Timeline (1972)
This is a series of photographs taken of "Kiss
II" (1974), an integral hologram produced by
Lloyd Cross, inventor of the process. The
hologram -- which was made from approximately 360
frames of motion picture footage -- was typically
mounted in a semi-circular, wall-mounted display
and illuminated by a single light bulb below. The
floating, 3-dimensional image of Pam Brazier
blows a kiss and winks as the viewer walks by.
(Photo by Daniel Quat, 1977)

• In 1972, Lloyd Cross developed the integral
  hologram by combining white-light transmission
  holography with conventional cinematography to
  produce moving 3-dimensional images. Sequential
  frames of 2-D motion-picture footage of a
  rotating subject are recorded on holographic
  film. When viewed, the composite images are
  synthesized by the human brain as a 3-D image.

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History of Holography Timeline (1972)

• 18" x 24" laser transmission hologram,
  "Hand in Jewels," produced in 1972 by Robert
  Schinella and the McDonnell Douglas Electronics
  Company, St. Louis, MO for Cartier, Inc., New
  York. The hologram appeared in Cartier's window
  on Fifth Avenue, projecting the hand out over the
  sidewalk to the astonishment of passers by.

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History of Holography Timeline (1983)

• In 1983 MasterCard International, Inc.
  became the first to use hologram technology in
  bank card security.

The first credit cards to carry embossed
holograms were produced by American Bank Note
Company, New York, for MasterCard International,
Inc. The 2-channel holograms were the widest
distribution of holography in the world at that
time.
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History of Holography Timeline (1984)

• National Geographic magazine was the first
  major publication to put a hologram on its cover.
  The March 1984 issue carried nearly 11 million
  holograms throughout the world.

Volume 165, Number 3, March 1984 had the first
hot stamped hologram embossed directly onto a
magazine cover, with an accompanying story, "The
Wonder of Holography." The 2 1/2" x 4" embossed
hologram of an eagle was produced in 1983 by
Kenneth A. Haines, Eidetic Images, Inc. Elmsford,
NY, a subsidiary of American Bank Note Company,
New York, NY. (Photo by Paul D. Barefoot, 1999)
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Basic terms and concepts in holography

• Interference
• The superposition or interference of two light
  waves (with same frequency) will emerge from the
  points R and O. Taking an object wave and
  reference wave without restriction to generality
• o oe-iF
• r re-i?
• The phase ? ?R - 2p(r1/?) is determined by the
  starting phase of the wave at point R and the
  phase change at distance r1. The same is valid
  for F Fo- 2p(r2/?).
• At point P, the complex amplitudes add up r o
  
• The intensity I is the square of the sum of the
  complex amplitudes
• I r o2 r.r o.o o.r
  r.o

r and o are the field amplitudes of the
respective waves at the point of superposition P
I r2 o2 r.o.e-i(F-?) ei(F-?)
I r2 o2 2. r.o.cos (F-?)
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Basic terms and concepts in holography

• If the light sources are emitting completely
  independently then the average of cos(F-?)
  vanishes since the phases vary statistically.
  This results in
• I r2 o2
• or I I1 I2
• In this case the waves are called incoherent.
  The intensities of both waves add up and
  interference does not occur.
• If the value of ?R-Fo does not change, the waves
  are coherent. Locations in space exist where
  cos(?-F)/-1. If the field strengths oscillate
  in the same phase () this results in
• r o and Imax r2 o2 2.r.o
• If they oscillate in opposing cycles (-) the
  resulting superposition is
• r o and Imin r2 o2 - 2.r.o

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Basic terms and concepts in holography

• Fresnel Zone Lens
• Points of objects close to the hologram reflect
  or emit spherical waves. Holograms of such
  objects waves have been known as Fresnel zone
  lenses.
• The point P which represents the object is
  located at the distance z0 from thr photographic
  layer. It emits a spherical wave. Additionally a
  plane reference wave r falls onto the layer. The
  interference pattern consists of concentric
  circles. For all points that have the same
  distance from the center of the photographic
  plate the incoming waves have the same phase. The
  path difference between the two interfering waves
  increases by one wavelength ? from one ring to
  the other (and the phase difference increases by
  2p). The path difference in the center can be
  taken to be zero. For the kth ring this results
  in the path difference k?, so that the ring
  radius can be written as

rk2 (z0 k?)2 z02 2 z0k? k2?2
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Basic terms and concepts in holography
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Basic terms and concepts in holography
The distance between the neighboring rings is
Try deriving this from the previous equation
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Basic terms and concepts in holography

• Each small area of the zone lens can be
  interpreted as a regular diffraction grating. The
  zeroth order diffraction is the weakened
  illumination beam. Additionally, for a sie-like
  grating diffraction of the order N /-1 occurs
  at the following angles

The deflection angle increases with the distance
from the hologram axis. It can be proved that the
hologram of a single point represents a Fresnel
zone lens by showing that the beams are
intersecting real and virtual at the distance z0
from the hologram plane. During reconstruction
the first order of diffraction forms a spherical
wave which creates an image point at the distance
z0 in front of the hologram. The -1st order of
diffraction is a divergent spherical wave with a
virtual image point at the distance z0 behind the
hologram.
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Basic terms and concepts in holography

• Visibility
• In holography r and o represent the
  reference and the object wave, respectively.
  During the recording of the hologram the
  visibility V in the interference field is given
  by the ratio of the two waves I1r2 and I2o2. It
  is defined by

For coherent waves, one gets
The visibility reaches a maximum of 1 at I1
I2
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Basic terms and concepts in holography

• Influence of Polarization
• For the preceding considerations concerning
  interference it was assumed that the polarization
  of the light waves is parallel. From that it
  follows that the maximal visibility of V1 holds
  for I1 I2. If the polarization directions of
  the two linearly polarized waves enclose an angle
  ? the following equations result-

I r2 o2 2ro cos(F-?) cos ?
and
No interference occurs if the directions of
polarization are perpendicular to each other the
visibility is 0. For optimal visibility object
and reference wave have to polarized parallel
each other. Even by using linearly polarized
light radiation this cannot always be achieved in
practice since light is being partly depolarized
when scattered at an object.
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Basic terms and concepts in holography

• Holographic Recording and Reconstruction
• The difference between photography and
  holography lies in the ability of holography to
  record the intensity as well as the phase of the
  object wave. It may seem almost incredible that
  the information of a three dimensional object,
  can be recorded into a two dimensional
  photographic layer. A look at the lectures on
  electrodynamics can help understand this
  principle if the amplitude and the phase of a
  wave are known in one (infinite) plane, the wave
  field is entirely defined in space.

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Basic terms and concepts in holography

• Recording
• The amplitudes of the object and reference wave
  on the photographic layer are given by o and r,
  respectively. These variables describe the
  intensity of the EM field of the light wave which
  impinges on the photosensitive layer. Both waves
  superpose, i.e. they form or. The intensity I is
  calculated as the square of the amplitude

I r o2 (ro)(ro)
I r2 o2 ro ro
The last term containing the object wave o is
important for holography. The darkening of the
holographic film is dependent on the intensity I.
Thus the information about the object wave o is
stored in the photographic layer.
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Basic terms and concepts in holography

• Reconstruction
• The reconstruction is performed by illuminating
  the hologram with the reference wave r. We will
  assume that the amplitude of transmission of the
  film material is proportional to I which is
  contrary to usual film processing. Therefore, the
  reconstruction yields the light amplitude u
  directly behind the hologram

u r.I r (r2 o2) rro r2o
u0 u-1 u1.
The object wave is itself reconstructed with
amplitude of the reference wave r2 being
constant over the whole hologram. This proves
that the object wave o can be completely
reconstructed. It represents the 1st diffraction
order.
Governs the reference wave which is weakened by
the darkening of the hologram by a factor of
(r2 o2) (zeroth diffraction order)
Describes the conjugate complex object wave o.
Corresponds to the -1st diffraction order.
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In-line Hologram (Gabor)

• The technique of straightforward holography
  developed by Gabor places the light source and
  the object on the axis perpendicular to the
  holographic layer. Only transparent objects can
  be considered. If an axial point O is chosen as
  an object emitting a spherical wave the resulting
  hologram for a plane reference wave is a Fresnel
  zone lens. The disadvantage of in-line or
  straightforward holograms is obvious during
  reconstruction the hologram is illuminated with a
  plane reference wave as shown in part (b) of the
  image. Since it represents a zone lens a virtual
  point appears at the same distance to the right
  of the hologram. During observation the two
  images lying on the same axis interfere which
  leads to image disturbances (shown in (b)).
  Moreover, the observer looks directly into the
  reconstruction wave. Because of these
  disadvantages this form of holography is only of
  historical interest.

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In-line Hologram (Gabor)
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Off-axis Hologram (Leith-Upatnieks)

• It turns out that it is more favorable to
  shift either the holographic layer or the object
  sideways. Laser beam, object, and hologram are
  not on the same axis anymore. The hologram
  represents the outer area of a fresnel zone lens.
  Again a virtual and a real image are formed
  during construction. The advantage of off-axis
  holography is that both images do not interfere
  during observation and image disturbances are
  avoided. By tilting the reference wave (or
  shifting the object) it is achieved that the
  three diffraction orders, namely the image, the
  conjugated image, and the illumination wave, are
  spatially separated. This has the advantage that
  also holograms of opaque objects can be produced
  since the reference wave is not obstructed by the
  object. In principle, a single beam or a multiple
  beam technique can be used.

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Fourier Hologram (Lensless)

• If the object O and the light source R are
  within the same plane parallel to the hologram,
  Fourier holograms are generated. This geometric
  condition can only be satisfied for plane
  objects. In a Fourier hologram the interference
  fringes appear as a set of hyperbolas whilst
  especially in in-line holograms circular sets in
  the form of Fresnel zone lenses appear. Like in
  all thin holograms two (real) images appear
  during reconstruction. The regular image is at
  the position of the original object the
  conjugated one appears in the same plane parallel
  to the hologram. The point light source R is the
  center of the point symmetry for the two images.

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Fraunhofer Hologram

• Fourier holograms are formed by the
  superposition of spherical waves whose centers
  have the same distance from the holographic
  layer. If the layer is moved far away the center
  depart and in the limit plane waves are created.
  
• This hologram type is especially used for
  the measurement and investigation of aerosols.
  The object with radius r0 has to be so small that
  a diffraction pattern will appear in the far
  field. The condition for the distance
  object/hologram is z0 gtgt r02/?

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Fraunhofer Hologram
This figure represents the Gabor holography
with the condition of diffraction being present
in the far field. The light of the primary image
is spead over such a large area in the conjugated
image that is appears as a weak even background.
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Reflection Hologram (Denisyuk)

• Until now holographs were presented at which
  the object and the reference wave impinge from
  the same side on the photographic layer.
  Holograms whose images are reconstructed in the
  reflection are of large importance especially in
  the field of graphics and art. In this case, the
  reference wave- and later the reconstruction
  wave- has to impinge from the observers side
  onto the hologram. The object wave in this type
  of recording impinges on the hologram from the
  opposite side.
• Of importance is the setup after Denisyuk in
  which the holographic layer is positioned across
  between the light source and the object. This
  results in the interference planes being almost
  parallel to the light sensitive layer.

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Reflection Hologram (Denisyuk)

• The distance of the grating planes when using
  a He-Ne or ruby laser is ?/2 0.3µm.
• Therefore, for a typical layer thickness of
  around 6µm, almost 20 grating planes fit into the
  light sensitive layer.
• So this system behaves like a thick grating.
• During reconstruction the illumination wave
  which is ideally identical to the reference wave
  is reflected at the grating planes. The virtual
  image of the object appears in the reflected
  light. Interference effects appear during the
  mirroring which lead to Bragg reflection. If
  white light is used for illumination only the
  wavelength used for the recording is reflected
  due to the Bragg effect. Therefore a sharp
  monochromatic image appears although white light
  is used for reconstruction. This is the advantage
  of thick reflection holograms which are called
  white light holograms.

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Reflection Hologram (Denisyuk)
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Summary of the holographs
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Formation of a hologram

• The basic technique of holograph formation is
  to divide the coherent light coming from a laser
  into two beams one to illustrate a subject and
  one to act as a reference.

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Formation of a hologram

• Reference wavefronts are often (but not
  necessarily) unmodulated spherical or plane
  fronts. The reference beam is directed so as to
  intersect the light transmitted or reflected by
  the subject. Assuming the two beams to be
  perfectly coherent, an interference pattern will
  form in the volume of space where the beams
  overlap. A photosensitive medium, placed in the
  overlap region, will undergo certain chemical or
  physical changes due to exposure to light
  intensity. After removal from the light and after
  any processing required to record these changes
  as an alteration of the optical transmission of
  the medium, the medium becomes the hologram.

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Basic holography equations

• The complex amplitude of light arriving at
  the plate from Object 1 can be expressed as a1
  a1exp(if1) where a1 and f1 are both functions of
  the spatial coordinates at the plate.
• Similarly, the complex amplitude of light
  arriving at the plate from Object 2 can be
  expressed as a2 a2exp(if2)
• The complex conjugates of a1 and a2 will be
  designated a1 and a2.

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Basic holography equations

• We find that the transmittance t of the
  completed hologram (the ratio of light
  transmitted by the hologram to that incident on
  it) contains a term tE proportional to the
  exposure E IPte and hence proportional to the
  intensity I.
• Summing the amplitudes a1 and a2 and
  multiplying the complex conjugate of the sum, we
  may write for the intensity
• I (a1 a2) (a1 a2)
• a1a1
  a2a2 a1a2 a2a1
• I1 I2 a1a2 a2a1
  
• We assume a linear relation between t and
  E, and consequently between t and I, of the form

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Holography in every day life
Microscopy When specimens of cells or
microscopic particles are viewed conventionally
under high magnification, the depth of field is
correspondingly small. A photograph that freezes
motion of the specimen captures in a focused
image a very limited depth of field within the
specimen. The disadvantages of this restriction
can be overcome if the photograph is a hologram,
which in a single snapshot contains potentially
all the ordinary photographs that could be made
after successive refocusings throughout the depth
of the living specimen. The image provided by the
hologram may be viewed by focusing at leisure on
any depth of an unchanging field. In making a
hologram with a microscope, the specimen is
illuminated by laser light, part of which is
first split off outside the microscope and routed
independently to the photographic plate, where it
rejoins the subject beam processed by the
microscope optics.
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Holography in every day life

• It can be shown that, if reconstructing light of
  wavelength ?r is longer than the wavelength of
  light ?s used in holographing the subject, a
  magnification is given by

where p is the object distance (subject from
film) and q is the image distance (image from
hologram). Object and image distances are equal
when the reference and reconstructing wavefronts
are both plane wave. However, if the hologram
were made with laser X-radiation and viewed with
visible light, magnifications as large as 106
could be achieved without deterioration in
resolution.
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Holography in every day life

• Holograms that simply redirect light may be used
  as inexpensive optical elements, serving in place
  of lenses and mirrors. To cite one popular
  application, laser readers of the universal
  product code on groceries use a spinning disc
  outfitted with a number of holographic lenses. By
  continuously providing many angles of laser
  scanning, the product code can be identified even
  when the item is passed casually over the
  scanner.

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Holography in every day life

• Holographic data storage also offers tremendous
  potential. Because data can be reduced by the
  holographic technique to dimensions of the order
  of the wavelength of light, volume holograms can
  be used to record vast quantities of information.
  As the hologram is rotated, new exposures can be
  made. Photosensitive crystals, such as potassium
  bromide crystals with color centers or the
  lithium niobate crystal, can be used in place pf
  thick-layered photoemulsions.
• Because information can be reduced to such tiny
  dimensions and crystal can be repeatedly exposed
  after small rotations that take place of turning
  pages, it is said that all the information in the
  Library of Congress could theoretically be
  recorded on a crystal the size of a sugar cube!

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Holography in every day life

• A telephone credit card used in Europe has
  embossed surface holograms which carry a monetary
  value. When the card is inserted into the
  telephone, a card reader discerns the amount due
  and deducts (erases) the appropriate amount to
  cover the cost of the call.

Supermarket scanners read the bar codes on
merchandise for the store's computer by using a
holographic lens system to direct laser light
onto the product labels during checkout.
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Holography in every day life
Another area in which holograms maybe very useful
is in pattern recognition. Briefly, the procedure
is as follows. A text is scanned, for example,
for the presence of a particular word or letter
to be identified in an appropriate optical
system. The presence of the letter is indicated
by the formation of a bright spot in a location
that indicates the position if the letter in the
text. The hologram acts as a matched filter,
recognizing and transmitting only that spatial
spectrum similar to the one recorded on it. The
technique can be applied to holographic reading
of microfilms, for example. Military applications
of include the use of a memory bank of holograms
of particular objects or targets constructed from
aerial photographs. Weapons could, by pattern
recognition, select proper targets. It has also
been suggested that robots could identify and be
directed toward appropriate objects in the same
way.

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Holography in every day life

• CNN Holograms Debut With Jessica Yellin Figure
  (must watch!!!)
• CNN Will I Am Hologram, First time on TV
• Just for fun!
• Holography as a measure to increase security

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Interesting articles to read on holography

• The Brightest, Sharpest, Fastest X-Ray Holograms
  Yet
• NTT Develops Stamp-Size 1GB Hologram Memory
• Quantum holography system
• Holographic Storage Overview at CNET
• Laser Pointer Holograms
• How Holographic Storage Works