The digitally reconstructed hologram

The hologram of the object, recorded by the CCD sensor is shown in figure 22. The recorded image has an unpredictable character which is given to it by the speckle field produced by the wave diffracted by the object.

Figure 22 : Digitally recorded hologram [zoom...]

When is chosen as the algorithm for reconstruction using the direct Fresnel transform, the digital focusing of the object is in the +1-order. The amplitude of the field numerically diffracted using points is shown in figure 23.

$Figure 23 : The diffracted field when dR = -660 mm$

Figure 23 : The diffracted field when dR = -660 mm [zoom...]

The image resolution is and and the sampling pitch is . The Reconstructed field covers an area of . Taking into account the theoretical elements p[resented in this course, the +1-order is located at the coordinates which correspond to the pixel coordinates .

When, is imposed,focusing is in the -1-order, the calculated fields having the same area as before. This is illustrated in figure 24.

$Figure 24 : The diffracted field when dR = +660 mm$

Figure 24 : The diffracted field when dR = +660 mm [zoom...]

Taking in to account the hermitian symmetric properties of the Fourier transform, the -1-order is flipped and located at the coordinates , which correspond to the pixel coordinates .

If a reconstruction distance other than , is chosen, the image will be blurred.

The animation shown in figure 25 illustrates the formation of the image based on the distance imposed by the algorithm of the Fresnel transform.

Figure 25 : Image focus depending on imposed distance (Animation)

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