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Hologram Technique After Photographic method...!!!TRANSCRIPT
HOLOGRAPHY
PRESENTED BY-
PRIYA SRIVASTAVA
090105801
E.I.E VIII SEM.
INTRODUCTION
Images of objects are generally obtained using photographic method.
In this method a lens focuses the light reflected from a three-dimensional object onto a
photographic film where a two-dimensional image of the object is
formed.
A –ve is first obtained by developing the film and then a
+ve is obtained through printing.
The +ve print is a two-dimensional record of light intensity received from the
object.
It contains information about the square of the amplitude of the light wave that produced the
image but information about the phase of the wave is not
recorded & lost.
In 1948 Dennis Gabor outlined a two-step lenseless imaging
process.
It is radically a new technique of
photographing the objects & is known as
wave front reconstruction.
The technique is also called holography.
The word holography is formed by combining
parts of two Greek words: ‘holos’, meaning
“whole”, & ‘graphen’ meaning “to write”.
Thus holography means writing the complete image.
HOLOGRAPHY MEANS:
It is a recording of interference pattern
formed between two beams of coherent light
coming from the same source.
In this process both the amplitude &
phase components of light wave are
recorded on a light sensitive medium
such as a photographic plate.
The recording is known as a hologram.
PRINCIPLE
Holography is a two-step process.
First step is the recording of
hologram where the object is
transformed into a photographic
record.
The second step is the
reconstruction in which the
hologram is transformed into
the image.
A Hologram is the result of interference occurring between two waves, an object beam which is the light scattered off the object & a coherent background, the reference beam, which is the light scattered off the object & a coherent background, the reference beam , which is the light reaching the photographic plate directly.
Making a Hologram
Beam splitter
mirror
mirror
Beam spreader
PROPERTIES
Photography, is an ordinary photograph each region
contains separate & individual part of the original object. Therefore, destruction of a
portion of a photographic image leads to an irreparable loss of information corresponding to
the destroyed part.
On the other hand, in a hologram each part contains information about the entire
object
Conventional photography vs. Holography
Conventional photography
2-d dimension of a 3-d scene
(object).
Photograph lacks depth perception.
Film sensitive only to intensity
distribution.
Conventional photography vs. Holography
Hologram:
3-d dimension of a 3-d scene. Not only the intensity distribution of reflected light is
recorded but also the phase distribution. To view a hologram, the wavefront is reconstructed.Viewed from different angles, the object is also seen from different angles.
Conventional photography vs. Holography
Hologram:
Converts phase information into amplitude information (in-phase - maximum amplitude, out-of-phase – minimum amplitude).
Interfere wavefront of light from object beam with a reference wave.
The hologram is a complex interference pattern . It’s a kind of diffraction grating.
If you tear a hologram in half, you can still see the whole image in each piece.The same is true with smaller and smaller pieces.
APPLICATIONS
Holographic Interferometer
Holography is widely used in non-destructive testing to study
distortions resulting from stresses, strains, heat & vibrations etc. In the
double exposure technique two exposures are made of the object, one before processing & the other
after.
Supermarket and department store scanners use a holographic lens
system that directs laser light onto the bar codes of the product.
The use of holograms on credit cards and debit cards provide added security to
minimize counterfeiting.
Medical doctors can use three-dimensional holographic CAT scans
to make measurements without
invasive surgery.
ACOUSTIC HOLOGRAPHY
It is easy to produce coherent sound waves. Sound waves readily propagate in solids.
Therefore, a three dimensional acoustical
hologram of an opaque object can be made.
By viewing such hologram in visible light the internal
structure of the object can be observed.
HOLOGRAPHIC OPTICAL ELEMENTS
Holographic optical elements (HOE) are diffractive devices
which are holograms of typical optical
components such as lenses or mirrors.
HOEs perform precisely the same type of operation as
the lenses or mirrors,
but they do it by diffraction and not by
refraction or reflection.
They are used in barcode scanners,
office copy machines, solar
concentrators, e.t.c.
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