Sand table for holography


(No photograph of the apparatus available)

Holography requires a vibration-free environment so that a laser beam can be split in such a fashion that a portion of the beam illuminates an object and is reflected onto a piece of film, and the other portion of the split beam shines directly on the film, with the result that the film records the interference pattern generated by recombining the two beams.  The film must be very fine grained because the interference pattern occurs on a very small scale, and the source, object, and film must be completely immobile during the exposure, which could last several seconds.  Any vibrations of the table surface during the exposure will destroy the interference pattern, and no hologram will result.

I constructed a vibration-free table by building a hollow box that measured 4 feet by 4 feet and which was 2 feet deep.  A massive base was built and the box was supported on this base by placing the box on four partially inflated motorcycle inner tubes.   The box was then filled with 1800 pounds of coarse, well-washed sand.  The great mass of the filled box, coupled with its relative isolation from the floor, created a low-vibration surface upon which the holographic components could be placed for generating a holographic image, provided the room was darkened for the exposure.  We had some success with this setup, but subsequently we have been able to obtain a professional air-suspension, low-vibration table which is designed for this and similar purposes, and so have replaced the sand table which I constructed.  Unfortunately, I do not think we took any photographs of the sand table while it was in use.