Eldon McLaughlin, age 14, of Niagara Falls, Ontario, Canada, for her question:
What is holography?
If you think that a photograph gives you a complete and accurate picture, you are mistaken. Compared with a holograph, it is a flat and lifeless distortion. Some¬day the new progress of holography may bring us vivid, three dimensional TV and photographs that look real as life itself.
In the past decade, scientists have tamed two fabulous new servants the laser beam and the hologram. Both manipulate light; and both have potentials beyond the imagination. Right now, these two servants are looking for work new problems to solve, new duties to perform. The laser concentrates the fanning spread of light into a narrow beam of intense brilliance. The hologram freezes the ordinary jumble of light waves and uses a laser beam instead of a camera lens to record a vivid, three dimensional picture of the scenery.
The electromagnetic energy of light pulses in wave lengths averaging 500 million million per second. That is five plus 14 zeros. Each color band of the spectrum has its personal range of wave lengths all fanning forth at 186,000 miles per second and cries crossing like a multitude of ripples on a pond. A camera photo¬graphs not the actual scene, but the jittering jumble of light waves from the scene. The crests and troughs of wave lengths interfere with each other. Where crests meet crests or where troughs coincide with troughs, they leave bright spots of light on the film. Where crests meet troughs, they cancel out the light and record infinitesi¬mal points of blackness.
Holography tames and regiments the normal bodge podge of wave interference. It uses a. laser to produce beams of pure color that can be rigidly directed and crossed at a precise angle. Beams of the same color pulse along on similar wave lengths. This eliminates the collisions between longer and shorter waves. The sub¬ject is illuminated with bright narrow laser beams and a reference beam from the same laser is mirrored to cut across them. It is angled to adjust the wave length interference so that crests and troughs cancel each other out evenly. The pulsing fallling on the screen of film are frozen. The room is dark and the laser spurts for a fraction of a second. Its regimented beams of pure color record a 3 D hologram, a total picture that looks real enough to touch. If you bend your head, you can see around objects in the foreground.
The hologram film is developed and viewed under a bright light adjusted to coin¬cide with the reference beam used to take the picture. A filter is used to recreate the color of the laser beams. When the light is focused on the hologram, the scene springs to life in vivid, unbelievable detail. What's more, dozens of other images may be superimposed on the film. The reconstruction beam is readjusted to bring them to life. It is possible to record the whole Bible on an inch square hologram.
At present, we are still learning to make the best use of holography. We expect it to be able to store a whole library in a few filing cabinets. It can help meteor¬ologists by charting the sizes, distribution and behavior of cloud droplets. It could sift and sort through 100,000 fingerprint records and identify the correct owner in one minute. Its use to future biologists is astounding. Sub microscopic organisms that live and move in sub seconds can be hologrammed and stored to be studied at leisure in vivid, 3 D depth. And these holographic miracles are merely a hint of what is to come.