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We report the enlargement of holograms by illuminating with a halogen lamp from the small format of 35mm. A special configuration is employed to concentrate the luminous energy on the projection lens. An enlargement factor of 20 was obtained in a 75cm x 114cm holographic screen.

Introduction.

The enlargement of holograms under white light was previously reported by Lunazzi1,2,3, and by Lunazzi and Boone4,5, but xenon arc lamps or very efficient holographic materials were needed. We report here the achievement of a large enlarging factor (20x) starting from the very small format of 35mm using commercially available holographic film. The main principle for it is that, since the light diffracted by the hologram is projected through a lens, it can be directed to it avoiding the enormous lost of light that is not usually directed to the projecting aperture of the lens. We make the hologram by imaging through a lens having a centered horizontal slit. When reconstructing, a white light beam illuminates the hologram in the opposite direction of the reference wave direction so that the conjugated image is reconstructed. All of the white light whose wavelength matches that of the laser light is re-directed to the aperture, while other wavelengths are horizontally diffracted aside to it. A proper position exists to diaphragm the lens in order to project all wavelengths back to where the object was, and at this position a holographic screen is located to distribute wavelengths according to the original view from the object. Spectral distribution of views when reconstructing the hologram.

As shown in Figure1, the hologram H is reconstructed by a white light beam RC whose direction is opposite to that of the original reference beam. To differentiate the wavelengths of the rays on the figure, they were dashed with a period that is proportional to its corresponding wavelength, so that red rays has longer segments than green and blue rays. We can see how some positions on the lens L can receive all wavelengths, while others can only receive part of the spectrum. A vertical slit selects a sample of all wavelengths. We achieve in this way the projection of all the horizontal perspectives A, B, C received at the lens going through the slit to be projected at the holographic screen H and being redistributed on its original sequence to give the final image of the object O.