Coherence Coherence Coherence Holography Recording Holography - - PDF document

Coherence Coherence Coherence

Holography Recording

• Laser beam is split in 2
• 1 wave illuminates the object
• The object scatters the light
• nto the hologram plate

(object wave)

• The other wave is reflected directly onto the hologram
• plate. (reference wave) constitutes a uniform illumination
• f the hologram plate
• The hologram plate must be a light-sensitive medium,

e.g. a silver halide film plate with high resolution

Holography Recording

• Let the object and

reference waves in the hologram plane be described by the field amplitudes uo and u.

• These two waves will interfere

resulting in an intensity distribution

• This intensity is allowed to blacken the hologram plate
• Then it is removed and developed
• This process is hologram recording

* u u u * u u u u u I

• 2
• 2

2

• +

+ + = + =

Holography Recording

• This hologram has a

transmittance t proportional to intensity distribution

* u u u * u u u I t

• 2
• 2

α α α α α + + + = =

• Replace the hologram back in the holder in

the same position

• Block object wave and illuminate the hologram with the reference

wave (reconstruction wave) Ua which will be U multiplied by t

[ ]

• 2
• 2
• 2

a

u u (uu) * u u u u u u α α α α + + + = = t

Holography Reconstruction

• The quantity

IuI2 is constant –

uniform light and the last term thus becomes (apart from a constant) identical to the original object wave uo.

• We are able to reconstruct the
• bject

wave, maintaining its

• riginal

phase and relative amplitude distribution uo

• by looking through the hologram, object can be seen in 3D

even though the physical object has been removed

• Therefore this reconstructed wave is also called the virtual

wave

Holography Reconstruction

• Replace the hologram back in the

holder in the same position

• Block object wave and illuminate

the hologram with the reference wave (reconstruction wave)

• We are able to reconstruct the
• bject

wave, maintaining its

• riginal

phase and relative amplitude distribution

• by looking through the hologram, object can be seen in 3D even

though the physical object has been removed

• Therefore this reconstructed wave is also called the virtual wave
• Direct wave: corresponds to zeroth order grating

diffraction pattern

• Object wave: gives virtual image of the object

(reconstructs object wavefront) – first order diffraction

• Conjugate wave: conjugate point, real image (not

useful since image is inside-out) – negative first order diffraction

• In general, we wish to view only the object wave – the
• ther waves just confuse the issue

Hologram Reconstruction Fringe analysis Fourier

• by tilting the reference wave in the second
• exposure. The fringe pattern is
• where fo is the carrier frequency in the x-

direction

• This equation can be rewritten as

Fringe analysis Fourier

then given by

Fourier spectra will be separated as shown By use of a filter function obtain C( fx, y) as shown in Figure 11. 11 (b). Next the inverse Fourier transform of this function is computed and as a result the complex function c(x, y) is obtained.