2 S.No.ModuleLectur e No. PPT Slide No. 1Basic principles of Holography L Construction and reconstruction Images On hologram. L Applications of Holography. L UNIT INDEX
3 Holography Holographyis about the photographic technique. The technic is called HOLOGRAPHY after the greek words HOLOS, and GRAPHOS, which mean complete, and writing respectively. It is the science of producing holograms. It is a form of photography that allows an image to be recorded in three dimensions.photography imagedimensions Lecture-3Lecture-3 Lecture-4
4 The technique of holography can also be used to optically store, retrieve, and process information. It is common to confuse volumetric displays with holograms, particularly in science fiction works such as Star Trek, Star Wars, Red Dwarf, and Quantum Leap.volumetric displays science fictionStar Trek Star WarsRed DwarfQuantum Leap
5 Technical description The difference between holography and photography is best understood by considering what a black and white photograph.It is a point-to-point recording of the intensity of light rays that make up an image. Each point on the photograph records just one thing, the intensity (i.e. the square of the amplitude of the electric field) of the light wave that illuminates that particular point.photographintensity lightamplitude electric field
6 In the case of a colour photograph, slightly more information is recorded (in effect the image is recorded three times viewed through three different colour filters), which allows a limited reconstruction of the wavelength of the light, and thus its colour.filterswavelengthcolour the holograms are recorded monochromatically. monochromatically
7 Holographic recording process To produce a recording of the phase of the light wave at each point in an image, holography uses a reference beam which is combined with the light from the scene or object (the object beam). If these two beams are coherent, optical interference between the reference beam and the object beam, due to the superposition of the light waves, produces a series of intensity fringes that can be recorded on standard photographic film.coherent interference superpositionphotographic film
8 These fringes form a type of diffraction grating on the film, which is called the hologram.diffraction grating The central goal of holography is that when the recorded grating is later illuminated by a substitute reference beam, the original object beam is reconstructed, producing a 3D image.
10 Holographic reconstruction process When the processed holographic film is illuminated once again with the reference beam, diffraction from the fringe pattern on the film reconstructs the original object beam in both intensity and phase (except for rainbow holograms where the depth information is encoded entirely in the zoneplate angle).diffraction zoneplate
11 Because many viewpoints are stored, each of the viewer's eyes sees the image from a slightly different angle, so the image appears three-dimensional. This is known as stereopsis.stereopsis The viewer can move his or her viewpoint and see the image rotate
16 A diffraction grating is a transparent or reflective sheet with thin slits, the distance between them and their diameter being on the order of the wavelength of the light. Light rays travelling towards it are bent at an angle determined by the distance between the slits and the wavelength of the light.diffraction gratingwavelengthrayswavelength Holograms as diffraction grating
17 When holograms are constructed, the reference beam and the object beam interfere with one another and the dark and light fringes of the interference pattern are recorded. interfereinterference pattern When this photograph is developed, the light parts become clear and the dark parts opaque.photograph
18 The clear, light parts become like the slits of a diffraction grating, and the angle at which they bend incoming light (the reconstruction beam) is determined by the spacing between them, which in turn was determined originally by the object beam and reference beam, when the hologram's interference pattern was made. Thus the slits bend the reconstruction beam to be the exact angles at each point that the object beam was going at.diffraction grating interference pattern
19 APPLICATIONS Holography can be applied to a variety of uses other than recording images. 1 Holographic data storage is a technique that 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. Lecture-6
20 As current storage techniques such as Blu-ray reach the denser limit of possible data density (due to the diffraction-limited size of the writing beams), holographic storage has the potential to become the next generation of popular storage media. Blu-raydiffraction The advantage of this type of data storage is that the volume of the recording media is used instead of just the surface.
21 APPLICATIONS 2. Digital holography An alternate method to record holograms is to use a digital device like a CCD camera instead of a conventional photographic film. This approach is often called digital holography.CCD In this case, the reconstruction process can be carried out by digital processing of the recorded hologram by a standard computer. computer A 3D image of the object can later be visualized on the computer screen or TV set.
22 APPLICATIONS 3.Use of holography in banknotes Holograms are used widely as a security device in many currencies such as the Brazilian real 20 note, British pound 5/10/20 notes, Canadian dollar 5/10/20/50/100 notes, Euro 5/10/20/50/100/200/500 notes, South Korean won 5000/10000 notes, Japanese yen 5000/10000 notes, etc.currencies Brazilian realBritish poundCanadian dollarEuro South Korean won Japanese yen
23 4. Holography in art Early on artists saw the potential of holography as a medium and gained access to science laboratories to create their work. Holographic art is often the result of collaborations between scientists and artists, although some holographers would regard themselves as both an artist and scientist.