o.i.ppt

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.

THAN

K

YOU

THAN

KYO

U..!

!!