Gabor Hologram

Axial hologram of the point source invented by D.Habor in 1948 was the first known type of holograms. Point source of light is places at the distance L from the photographic plate which is illuminated also by coherent flat wave. As a result the interferometric pattern, which appears in the place of the screen S, is stored on a photographic plate. Such a plate is called the hologram. Contrary to photography a hologram stores not only the information about the intensity of the waves coming from the source, but also about the phases of these waves. When a hologram is illuminated by coherent light the image is reconstructed in the same place where the source was located. In addition to apparent image P₁of the point source there are symmetrically situated a real image P₂ of the point as well as the part of the initial flat wave passed through the hologram.

Transmission of the Gabor hologram could be written as: t(x,y) ~ 1 + cos {k (x²+y²+L²)^1/2} , i.e. it is a system of concentric light and dark rings with radii R_m=(mλL)^1/2. This is fully coincides with radii of the rings in Fresnel zone plate. The only exclusion is that in Gabor hologram the transmission between the rings is not just 0 or 1, but changed smoothly according to harmonic law. As a result the Fresnel zone plate has many focal distances F_n=F/(2n+1), where n is any digit, while the sinusoidal zone plate based on the Gabor hologram principle has only the single focal distance.

For investigation of the focusing properties of Gabor hologram we can use an ordinary tungsten light bulb. Let us place the bulb at the distance L = 3-10 m from the hologram and the screen will be placed in the focus of hologram. In this case we can see on the screen the image of the glower. Taking into account that the bulb is situated rather far, but not in the infinity, the screen has to be moved at the distance ~ F²/a ≤ 1 cm from the focus away of hologram.

The photography of the glower focused by sinusoidal zone plate (Gabor hologram).

Experimental set-up for investigation of
focusing properties of Gabor hologram.

To utilize all the resolution of the hologram the size of the light source d should be rather small. So small, that the spatial coherence length Lλ/d at the hologram would be less than the diameter of the bigger ring. It means that with the parameters of the set-up given above the size of the source should be about the parts of millimeter. Diameter of the glower of a small bulb suits to this requirement. For this reason every part of the glower produces rather sharp image in the corresponding point of the focal plane. Because the light of the bulb is not monochromatic, the components at different wavelengths will be focused in different points. To avoid this the color filter should be placed in front of the bulb.

We fabricate and accept the orders for Gabor hologram HH-20-4000s and HH-30-4000s with focal distances 20 and 30 sm respectively. The hologram of size 16,3 x 11,9 mm is placed in the frame of the slide 35 x 38 mm (see photo in the left side of the screen). Thickness of the film is 0,11 mm. Resolution of the digital printing is 4000 dpi (point size is 6,35 microns). If you have any questions, please contact us: info@physics.nad.ru