PRINCIPLES OF HOLOGRAPHY

Historical Development :

• Gabor (1948 - no lasers) - developed holography for microscopy - won Nobel Prize
• Leith & Upatnieks (1961 - lasers) - Off-axis holography
• Stetson (1965) - Holographic Interferometry

Experimental Setup :

The traditional setup for making a hologram is shown below. The hologram is formed by the interference of two coherent light beams, one called the Reference Beam, and the other called the Object beam. Generally, set up coordinate system (x,y,z) with film plate in (x,y) plane at z = 0. The (x,y) coordinates are referred to as (p,q) for points in the z = 0 plane.

Object Beam :

Reference Beam :

Sum of fields on plate at (z = 0) :

Now if we want to reconstruct the hologram, we must remove the Object Beam and substitute a Reconstruction Beam I_C for the Reference Beam I_R (actually the Reference and Reconstruction Beams are usually the same) :

Transmittance Function T(p,q) of the holographic plate now needed :

Hologram Reconstruction :

Multiplying I_R by the transmittance function T, get five terms, of which the fifth one is

which gives a virtual image and is produced by the primary beam.

The fourth term is same as the fifth, except that the exponential is the negative of the one in the fifth term. This is very significant, as it produces a real, phase-inverted image referred to as the real pseudoscopic image in the secondary beam.

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