Death to Death Rays

The problems and powerful potential of the split atom already seem old hat; laser is now the word for the future in half the world's laboratories. The almost magical optical-electronic devices are said to be sparkling with more possibilities than scientists can begin to count. But Austrian Physicist Hans Thirring gets particularly exasperated when loose talk conjures up images of long-distance death rays capable of killing incoming missiles, or of laser light broiling earth-side cities from bases on the moon.

Familiar pictures of lasers burning holes in diamonds (TIME, April 20, 1962) are no proof at all of death ray capability. Such feats, Thirring protests in Britain's New Scientist magazine, are accomplished by concentrating a powerful flash of laser light on a tiny area by means of a lens. It is a nice trick in a laboratory, but warheads plunging down from space hardly can be expected to carry lenses to expedite their own destruction. To fuse a steel casing weighing 100 Ibs. would require a laser light strong enough to deliver 807 kilowatts of energy to it for a full minute. If the beam were to hit the warhead 30 miles above the earth, it would be spread out so much that only 0.5% of its energy would be effective. Thus the power of the whole beam--even without allowing for dimming as it passes through the atmosphere--would have to be 161,400 kilowatts, enough electricity for a city of 1,000,000 people and about 100 billion times the power of existing lasers.

Laser death rays would need even more power if they were based on the moon--where power is in short supply. Dr. Thirring figures that after traveling from the moon, even the best-focused laser beam would cover a circle on the earth two miles in diameter. Even the light of a 1,000,000-kilowatt moon-based laser would increase the natural sunlight on this large area by only 10% . To do appreciable damage to one earthly city would call for a lunar powerhouse many times larger than any that has ever been built on earth.

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