kuli ah ke 13 opt e holography

8/10/2019 Kuli Ah Ke 13 Opt e Holography

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Optik Terapan: HolographyKuliah ke 13


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Holografi:

Teori dikembangkan oleh seorang Ahli bernamaDennis Gabor pada tahun 1947 dan

mememangkan hadial Nobel pada Tahun 1971

Asal Kata : Holography di ambil dari bahasaYunani, kata hlos, "whole/seluruh" + graf,

"writing, drawing/menulis


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3

History of Holography

Invented in 1948 by Dennis Gabor for use inelectron microscopy, before the invention of thelaser

Leith and Upatnieks (1962) applied laser light toholography and introduced an important off-

axis technique


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Whats holography?

Holografi adalah sebuah proses atau teknikmembuat gambar / image 3 Dimensi daribenda.

Sebuah Hologram dihasilkan karena interaksi duacahaya laser.

Satu cahaya laser datang melalui benda ke film

/recorder Cahaya yang lain adalah cahaya referensi yangdatang langsung dari sumbernya ke film.


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For a better understanding of the process, it isnecessary to understand interferenceanddiffraction

Interferensi terjadi jika satu atau lebih mukagelombang berimpit atau bertemu.

Difraksi terjadi bila sebuah muka gelombangmembentur sebuah benda.

Physics of Holography


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Principle of Holography

Selama proses perekamam, object wave (gelombang yangmenyinari benda) dan reference wave (datang langsung daribenda) berinterferensi dalam bidang medium perekaman danmenghasilkan frinji interferensi. This photographic plate yangmenyimpang pola ini disebut Hologram.

Frinji Interferensi ini mengandung semua informasi tentangintensitas dan fase dari cahaya yang di hamburkan oleh benda.

Dalam Proses Rekonstruksi, hologramnya bertindak sepertisebuah kisi difraksi. Ini disinari oleh sebuah gelombang yangdisebut gelombang rekonstruksi. (n most cases this is similar tothe reference wave used for recording the hologram) and theimage of the object is reconstructed from the hologram.


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Merekam dan Melihat Hologram


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Konstruksi Suatu Hologram Membutuhkan Sebuah Laser (sumber cahaya yang koheren dan

monokromatik), lpembagi sinar, lensa cermin, film Fotografi, dan sebuahobjek atau benda.

Pembagi Sinar memisahkan cahaya laser menjadi dua berkas cahaya; Berkasreferensi dan berkas untuk benda.

Reference beam aimed at a piece of holographic film by mirrors. Object beam directed at object to be recorded to illuminate object and then

meets reference beam at film.

Menghasilkan pola interferensi dari berkas benda dan referensi yang

kemudian di rekam.

Film is developed./dicuci, hasilnya disebut hologram.

Hologram ni mengandung semua informasi tentang intensitas dan fase darigelombang-gelombang yang dihamburkan oleh objek/benda.


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Construction of HologramConstruction of Holograms


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Rekonstruksi sebuah Bayangan/gambar darisebuah hologram

To view the image, the hologram is again illuminated with anotherlaser beam called the reconstruction beam which is at same angle asreference beam.

Hologram acts as a diffraction grating.

This form a real image in front of the hologram and a virtual imagebehind the hologram.

The virtual image has all the characteristic of the object. The realimage can be photographed directly without using a lens.


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Reconstruction of an image from Hologram


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Hologram of a point source

Construction of the hologram of a point source

Any object can be represented as a collection of

points

Reference wave -

plane

Photosensitive plate

1. Records

interference

pattern (linear

response)

2. Emulsion has

small grain

structure ( )

Object wave - spherical

Photographic

plate

x

z

y


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13

Point object hologram construction:

Intensity distribution on plate

Reference wave

Object wave

Intensity distribution on plate

ROORRROOROyxI

zyxrwhere

oeezyxozyxO

reezyxrzyxR

ikrzyxi

ikzzyxi

****2

222

),,(

),,(

),(

),,(),,(

),,(),,(


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Hologram construction

)cos(2),(

0

)cos(2),,(

22

22

krororyxI

planef ilmz

ororzyxI

Maxima for kr=2m or r=m

i.e. if the OPL difference OZ OP is an integral number of

wavelengths, the referencebeam arrives at Pin step with the

scattered (i.e. object)beam.

Gabor zone

plate


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Hologram reconstruction

When illuminated by a coherent wave, A(x,y), known asthe reconstructionwave, the optical field emerging fromthe transparency is,

i.e. a superposition of 4 waves

If A(x,y)=R(x,y), i.e. reconstruction and reference wavesare identical,

ORBOBRRBOOttyxR

ABORRABOABOOAttyxA

bp

bp

2*2*

***

)(),(

),(


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17

Hologram reconstruction

Three terms in the reconstructed wave

ORBOBRRBOOttyxR bp2*2*

)(),(

Direct wave

identical to

reference waveexcept for an

overall change in

amplitude

Object wave

identical to object

wave except for a

change in intensity

Conjugate wavecomplex

conjugate of

object wave

displaced by a

phase angle 2


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18

Hologram reconstruction Three terms in the reconstructed wave of thepoint hologram

ikrikrkziikz

bp erBeBeeoBttyxR

222

)(),(

Direct wave

identical to

reference

wave

(propagates

along z)

except for an

overall change

Object wave

Spherical waveexcept for a

change in

intensity B|r|2i.e. reconstructed

wavefront

Conjugate wave

spherical wavecollapsing to a

point at a

distance z to the

right of the

hologram


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19

Direct, object and conjugate waves

Virtual

image

Real image

-z z

Direct wave

Object

wave

Conjuga

te wave

z=

Reference

wave


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Hologram :Direct, object and conjugate waves

Direct wave: corresponds to zeroth order gratingdiffraction pattern

Object wave: gives virtual image of the object(reconstructs object wavefront) first orderdiffraction

Conjugate wave: conjugate point, real image (notuseful since image is inside-out due to negative

phase angle) first order diffraction In general, we wish to view only the object wave

the other waves just confuse the issue


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21Off-axis- Direct, object and conjugate waves

Virtual

image Real image

Direct wav

Object

wave

Conjuga

te wave

Reference

wave

Use an off-axis system to record the hologram, ensuring separation of the three waves on reconstruction


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Transmission hologram: reference and object wavestraverse the film from the sameside

Reflectionhologram: reference and object waves

traverse the emulsion from oppositesides

HologramReflection vs. Transmission

View inTransmission View inreflection


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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 differentwavelengths 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)


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Holography vs. Photography

Photography is 2D record of a 3D object whereas holography gives athree dimensional form of original object. If any object is hidden justbehind another object then the observer can see the hidden object inviewing the hologram.

Hologram is the positive pattern whereas in conventional photographynegative pattern is produced.

In ordinary photography each region contains separate and individualpart of the original object. Destruction of a portion of a negative leads to

an irreparable loss of information corresponding to the destroyed part.On the other hand, each part of a hologram contains information aboutthe entire object. Destruction of a part of hologram does not cause a lossof information about the object, each separate fragment is capable ofproducing image with a reduced clarity.


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Holography vs. Photography (contd)

The information holding capacity of a hologram isextremely high by recording several images of theobject whereas in ordinary photography a photofilmcannot be used to record several images.

Without the knowledge of the reference wavefrontthe hologram cannot be deciphered/read.

Holography vs. Photography


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Although there are no actual dots in a hologram, it could be

said that each of a hologram's "dots" contains the whole image.


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Views from different angles of the image reconstructed

by a hologram, showing changes in perspective.


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Applications of Holography

Mendesain Kontainer untukmenyimpan material nuklir

Kartu Kredit yang membawa

nilai mata uang Supermarket scanners

Optical Computers

Improve design of aircraftwings and turbine blades

Used in aircraft heads-updisplay

Art/Seni

Archival Recording of fragilemuseum artifacts/ Perekamanbarang museum yangsensitif/peka


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Applications of Holography

Microscopy M = r/s Increase magnification by viewing hologram with

longer wavelength

Produce hologram with x-ray laser, when viewed withvisible 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 l)

E.g. stress points, wings of fruit fly in motion,compression waves around a speeding bullet,convection currents around a hot filament


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Star Wars : Obi-Wan - Hologram

kuli ah ke 13 opt e holography

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