INTRODUCTION In this method a lens focuses the light reflected from a three- Images of objects are generally dimensional object onto aobtained using photographic method. 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.It contains information about the square of the amplitude of the The +ve print is a two- light wave that produced the dimensional record of lightimage but information about the intensity received from the phase of the wave is not object. recorded & lost.
It is radically a newIn 1948 Dennis Gabor technique of outlined a two-step photographing the The technique is also lenseless imaging objects & is known as called holography. process. wave front reconstruction.
The word holography is formed by combining parts of two Greekwords: „holos‟, meaning “whole”, & „graphen‟ meaning “to write”.Thus holography means writing the complete image.
HOLOGRAPHY MEANS: In this process both It is a recording of the amplitude & interference pattern phase components formed between The recording is of light wave are two beams of known as a recorded on a light coherent light hologram. sensitive medium coming from the such as a same source. photographic plate.
PRINCIPLE Holography is a two-step process.The second step First step is the is the recording ofreconstruction in hologram where which the the object is hologram is transformed intotransformed into a photographic the image. record.
A Hologram is the result ofinterference occurring between twowaves,an object beam which is the lightscattered off the object & a coherentbackground,the reference beam, which is the lightscattered off the object & a coherentbackground, the reference beam ,which is the light reaching thephotographic plate directly.
PROPERTIES Photography, is an ordinary photograph each region contains separate & individual part of the original object. Therefore, destruction of aportion 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. HolographyConventional photography 2-d dimension Film sensitive of a 3-d scene only to intensity (object). distribution. Photograph lacks depth perception.
Conventional photography vs. HolographyHologram: 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 isalso seen from different angles.
Conventional photography vs. HolographyHologram: 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 Holography is widely used in non- destructive testing to study distortions resulting from stresses, strains, heat & vibrationsHolographic Interferometer etc. In the double exposure technique two exposures are made of the object, one before processing & the other after.
Supermarket and The use of holograms Medical doctors can department store on credit cards and use three-dimensional scanners use a debit cards provide holographic CAT scans holographic lens added security to to make system that directs minimize measurements withoutlaser light onto the bar counterfeiting. invasive surgery. codes of the product.
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 HOEs perform diffractive devices precisely the same which are holograms type of operation as of typical optical the lenses or components such as mirrors, lenses or mirrors. They are used in but they do it by barcode scanners, diffraction and not by office copy refraction or machines, solar reflection. concentrators, e.t.c.