holography (2)
TRANSCRIPT
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SUBMITTED TO:- SUBMITTED
BY:- MR:-BHARPUR SINGHHIMANSHU YADAV
ROLL NO. B53
B.TECH (ECE)
REG NO.10906992
SEC: C6904
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ACKNOWLEDGMENT
I would like to express my gratitude to all those who gave me the possibility to complete this
term paper. I want to thank the Department of ECE of LOVELY PROFESSIONAL
UNIVERSITY for giving me permission to commence this Term paper, to do the necessary
research work and to use departmental data. I have furthermore to thankMr. BHARPUR SINGH
who gave and confirmed this permission and encouraged me to go ahead with my term paper.
I am again deeply indebted to all my friends whose help, stimulating suggestions and
encouragement helped me in all the time of research for and writing of this term paper.
THANK YOU.
HIMANSHU YADAV
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HOLOGRAPHYContents
1. Introduction
2. History
3. Theory
3.1 Interference and diffraction
4.Working of a Hologram
5. Making a Hologram
6.Conventional vs. Holographic photography
7.Applications
7.1 Data storage
7.2 Security
7.3 Art
7.4 Games
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7.5 Other applications
8. Reference
1.INTRODUCTION
Holography
Holography (from the Greek, -hlos whole + -
graf writing, drawing) is a technique that allows the
light scattered from an object to be recorded and later
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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 thesame way as if the object were still present, thus making
the recorded image (hologram) appears three
dimensional.
1. History of Holography
Invented in 1948 by Dennis Gabor for use in electron
microscopy, before the invention of the laser
Leith and Upatnieks (1962) applied laser light to
holography and introduced an important off-axis
technique.
2.Theory
Though holography is often referred to as 3D
photography, this is a misconception. A better
analogy is sound recording where the sound field is
encoded in such a way that it can later be
reproduced. In holography, some of the light
scattered from an object or a set of objects falls on
the recording medium. A second light beam, known
as the reference beam, also illuminates the recording
medium, so that interference occurs between the
two beams. The resulting light field is an apparently
random pattern of varying intensity which is the
hologram. It can be shown that if the hologram is
illuminated by the original reference beam, a light
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field is diffracted by the reference beam which is
identical to the light field which was scattered by the
object or objects.
3.1 Interference and diffraction
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The interference fringes in a hologram cause light
to scatter
in all directions, creating an image in the process.
The fringes diffract and reflect some of the light
(inset),
and some of the light passes through unchanged.
Interference occurs when one or more wave fronts aresuperimposed. Diffraction occurs whenever a wavefront
encounters an object. The process of producing a
holographic reconstruction is explained below purely in
terms of interference and diffraction.
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The light that reaches the holographic emulsion is just like the waves in
the aquarium. It has peaks and troughs, and some of the waves are taller
while others are shorter. The silver halide in the emulsion responds tothese light waves just like it responds to light waves in an ordinary
photograph. When you develop the emulsion, parts of the emulsion that
receive more intense light get darker, while those that receive less
intense light stay a little lighter.
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3.Working of a Hologram
There are lots of different ways to arrange these tools -- we'll stick to
a basic transmission hologram setup for now.
1. The laser points at the beam splitter, which divides the beam of
light into two parts.
2. Mirrors direct the paths of these two beams so that they hit
their intended targets.
3. Each of the two beams passes through a diverging lens and
becomes a wide swath of light rather than a narrow beam.
4. One beam, the object beam, reflects off of the object and onto
the photographic emulsion.
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5. The other beam, the reference beam, hits the emulsion without
reflecting off of anything other than a mirror.
Working of a hologram can easily be understand by the
following diagrams
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In holography, light passes through a shutter and
lenses before striking a light-sensitive piece of
holographic film.
4. Making a Hologram
It doesn't take very many tools to make a hologram. We
can make one with:
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A laser: Red lasers, usually He-Ne) (helium-neon
lasers), are common in holography. Some home
holography experiments rely on the diodes from red laser
pointers, but the light from a laser pointer tends to beless coherent and less stable, which can make it hard to
get a good image. Some types of holograms use lasers
that produce different colors of light as well. Depending
on the type of laser you're using, you may also need a
shutter to control the exposure.
Lenses: Holography is often referred to as "lensless
photography," but holography does require lenses.However, a camera's lens focuses light, while the lenses
used in holography cause the beam to spread out.
A beam splitter: This is a device that uses mirrors
and prisms to split one beam of light into two beams.
Mirrors: These direct the beams of light to the correct
locations. Along with the lenses and beam splitter, themirrors have to be absolutely clean. Dirt and smudges
can degrade the final image.
Holographic film: Holographic film can record light at
a very high resolution, which is necessary for creating a
hologram. It's a layer of light-sensitive compounds on a
transparent surface, like photographic film. The
difference between holographic and photographic film isthat holographic film has to be able to record very small
changes in light that take place over microscopic
distances. In other words, it needs to have a very fine
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grain. In some cases, holograms that use a red laser rely
on emulsions that respond most strongly to red light.
5. Conventional vs. Holographic photography
Conventional:
2-d version of a 3-d scene
Photograph lacks depth perception or parallax
Film sensitive only to radiant energy
Phase relation (i.e. interference) are lost
Hologram:
Freezes the intricate wave front of light that
carries all the visual information of the scene
To view a hologram, the wavefront is
reconstructed
View what we would have seen if present at the
original scene through the window defined by
the hologram
Provides depth perception and parallax
Converts phase information into amplitude
information (in-phase - maximum amplitude,out-of-phase minimum amplitude(s
Interfere wavefront of light from a scene with a
reference wave
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The hologram is a complex interference pattern
of microscopically spaced fringes
holos Greek for whole message
If we tear a hologram in half, we can still see the
whole image in each piece. The same is true with
smaller and smaller pieces.Though its not so in
conventional photography.
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6.Applications
1. Data storage:-Holographic data storage is a techniquethat can store information at high density inside crystals or
photopolymers. The ability to store large amounts of information in
some kind of media is of great importance, as many electronic
products incorporate storage devices. The advantage of this type of
data storage is that the volume of the recording media is used instead
of just the surface.
2. Security:- Security holograms are very difficult to forgebecause they are replicated from a master hologram which requires
expensive, specialized and technologically advanced equipment. They
are used widely in many currencies such as the Brazilian real 20
note,etc.
3. Art:- . Holographic art is often the result ofcollaborations between scientists and artists,
although some holographers would regard
themselves as both an artist and scientist.
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4. In the future, we may be able to use hologramsto do everything from watching TV to deciding
which hair style will look best on us.
5. Games :- various video games are based on theholography principle.Such as HALO,DEAD SPACE etc
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6. Other applications
Holographic scanners are in use in post offices,
larger shipping firms, and automated conveyor
systems to determine the three-dimensionalsize of a package. They are often used in
tandem with checkweighers to allow
automated pre-packing of given volumes, such
as a truck or pallet for bulk shipment of goods.
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7. REFERENCES:-1. WWW .GOOGLE .CO .IN /HOLOGRAPHY /PHY .COM
2. WWW .PHYEDU .COM
http://www.google.co.in/HOLOGRAPHY/PHY.COMhttp://www.phyedu.com/http://www.google.co.in/HOLOGRAPHY/PHY.COMhttp://www.phyedu.com/