Coherence Coherence Coherence Holography Recording Holography - PDF document

Coherence Coherence Coherence

Holography Recording Holography Recording � Let the object and � Laser beam is split in 2 reference waves in the hologram � 1 wave illuminates the object plane be described by the field � The object scatters the light amplitudes u o and u. onto the hologram plate � These two waves will interfere resulting in an intensity distribution (object wave) 2 2 2 = + = + + + The other wave is reflected directly onto the hologram � I u u u u u * u u u * o o o o plate. (reference wave) constitutes a uniform illumination � This intensity is allowed to blacken the hologram plate of the hologram plate � Then it is removed and developed � The hologram plate must be a light-sensitive medium, � This process is hologram recording e.g. a silver halide film plate with high resolution Holography Recording Holography Reconstruction IuI 2 is constant – � The quantity � This hologram has a uniform light and the last term thus transmittance t proportional to becomes (apart from a constant) intensity distribution identical to the original object 2 2 = α = α + α + α + α t I u u u * u u u * wave u o . o o o � Replace the hologram back in the holder in � We are able to reconstruct the object wave, maintaining its the same position � Block object wave and illuminate the hologram with the reference original phase and relative wave (reconstruction wave) U a which will be U multiplied by t amplitude distribution u o [ ] by looking through the hologram, object can be seen in 3D � 2 2 2 = t = α + α + α + α u u u u u u * (uu) u u even though the physical object has been removed a o o o � Therefore this reconstructed wave is also called the virtual wave

Holography Reconstruction Hologram Reconstruction � Replace the hologram back in the • Direct wave: corresponds to zeroth order grating holder in the same position diffraction pattern � Block object wave and illuminate the hologram with the reference • Object wave: gives virtual image of the object wave (reconstruction wave) (reconstructs object wavefront) – first order diffraction � We are able to reconstruct the • Conjugate wave: conjugate point, real image (not object wave, maintaining its original phase and relative useful since image is inside-out) – negative first order amplitude distribution diffraction � by looking through the hologram, object can be seen in 3D even • In general, we wish to view only the object wave – the though the physical object has been removed other waves just confuse the issue � Therefore this reconstructed wave is also called the virtual wave 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( f x , 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.