1. Holography

2. 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

3. Conventional vs. Holographic photography
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

4. Conventional vs. Holographic photography
Hologram:
Freezes the intricate wavefront 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

5. Conventional vs. Holographic photography
Hologram:
Converts phase information into amplitude information (in-phase - maximum amplitude, out-of-phase – minimum amplitude)
Interfere wavefront of light from a scene with a reference wave
The hologram is a complex interference pattern of microscopically spaced fringes
“holos” – Greek for whole message

6. Hologram of a point source
Construction of the hologram of a point source
Any object can be represented as a collection of points
Photographic plate
Photosensitive plate
Records interference pattern (linear response)
Emulsion has small grain structure ()
Reference wave - plane x z
Object wave - spherical y

7. Working Principle

8. Continues..

9. Creating Holograms

10. Pattern left on media

11. Reconstructing the image

12. Point object hologram construction: Intensity distribution on plate
Reference wave
Object wave
Intensity distribution on plate

13. Hologram construction
Maxima for kr=2m or r=m
i.e. if the OPL difference OZ – OP is an integral number of wavelengths, the reference beam arrives at P in step with the scattered (i.e. object) beam.

14. Hologram
When developed the photographic plate will have a transmittance which depends on the intensity distribution in the recorded plate
tb – backgrond transmittance due to |R|2 term
B – parameter which is a function of the recording an developing process

15. Hologram reconstruction
When illuminated by a coherent wave, A(x,y), known as the reconstruction wave, the optical field emerging from the transparency is,
i.e. a superposition of 4 waves
If A(x,y)=R(x,y), i.e. reconstruction and reference waves are identical,

16. Hologram reconstruction
Three terms in the reconstructed wave
Direct wave – identical to reference wave except for an overall change in amplitude
Object wave – identical to object wave except for a change in intensity
Conjugate wave – complex conjugate of object wave displaced by a phase angle 2 

17. Hologram reconstruction
Three terms in the reconstructed wave of the point hologram
Direct wave – identical to reference wave (propagates along z) except for an overall change in amplitude
Conjugate wave – spherical wave collapsing to a point at a distance z to the right of the hologram
a real image
displaced by a phase angle 2kz
Object wave – Spherical wave except for a change in intensity B|r|2
i.e. reconstructed wavefront

18. Hologram: Wavelength
With a different color, the virtual image will appear at a different angle – (i.e. as a grating, the hologram disperses light of different wavelengths at different angles)
Volume hologram: emulsion thickness >> fringe spacing
Can be used to reporduce images in their original color when illuminated by white light.
Use multiple exposures of scene in three primary colors (R,G,B)

19. Hologram: Some Applications
Microscopy M = r/s
Increase magnification by viewing hologram with longer wavelength
Produce hologram with x-ray laser, when viewed with visible light M ~ 106
3-d images of microscopic objects – DNA, viruses
Interferometry
Small changes in OPL can be measured by viewing the direct image of the object and the holographic image (interference pattern produce finges  Δl)
E.g. stress points, wings of fruit fly in motion, compression waves around a speeding bullet, convection currents around a hot filament

21. Capacity: 700 mb
Capacity: 4.7 Gb
Capacity: Gb
Capacity: 1-4 Tb

22. What is Holographic Memory ?
It is a memory that can store information in form of holographic image.
It is a technique that can store information at high density inside crystals or photopolymers.
It provides data to be written beneath the surface of the disc.
Holographic memory can store up to 1 Tb in a storage medium the size of a sugar cube crystal.

23. Why do we need this ?
“For Internet applications alone, industry estimates are that storage needs are doubling every 100 days”
By the year 2010, a storage system serving an average LAN will need … 100 TB and a WAN server will require 10TB to 1 petabyte …of storage” (Red Herring)

24. Basic Components spatial light modulator To direct the laser beams
LCD panel
To direct the laser beams
photopolymer
Lithium-niobate crystal
Mirrors
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In order to grow organically, banks need to focus on increasing the value of their existing customer relationships.
Beam splitters
CCD camera
To spilt the laser beam
Interprets the digital information
Blue-green argon laser

25. Properties of Hologram
A block or sheet of photosensitive material which records the diffraction of two light sources.
A laser beam is splatted into two beams:
Source beam
Reference beam
The two beams diffracts to form the image on the recording medium

26. Spatial light modulator
It is used for creating binary information out of laser light.
It is a 2D plane, consisting of pixels which can be turned on and off to create binary 1.s and 0.s.
It contains a two-dimensional array of windows, which are only microns wide.

27. Page Data Access
As the data is stored in the form of holograms, data retrieval must be in the same form.
So, a holographic system sends data in the form of pages.
It provides fast access times.

28. Error Correction
As the density of data is massive, it is prone to errors.
Errors can be controlled by:
Recording errors
Page level parity bits
Interfacing

29. Interfacing
While reading the data, they are sent to the computer as sheets.
Such thing may exceed the processor throughput
Remedy: Defining set of rules which can be used for correction and reading of data efficiently.

30. Future Computer Systems
Applications 1
Data Mining 2
Petaflop Computing 3
Future Computer Systems 4

31. Future Built on technology that’s around for 40+ years
Holographic Memory is the future of data storage
HUGE capacity, Very fast, Smaller
Parallel processing
Current storage methods nearing there fundamental limits of storage density
Large market and little new competition