The Quantum Age by Clegg Brian

Author:Clegg, Brian [Clegg, Brian]
Language: eng
Format: epub, pdf
Publisher: Icon Books
Published: 0101-01-01T00:00:00+00:00

CHAPTER 7

Making light work

It was inevitable that at the press conference to announce the first laser, the press corps would think of that science fiction staple, the ray gun. Here was a very powerful beam of light that surely would soon be made into a weapon. Only a remarkably short period of time, just four years, elapsed between the first experimental laser being produced and James Bond’s archetypal experience in Goldfinger where the ruby red beam cuts through a block of gold as if it were butter, heading inexorably towards splitting the immobilised Sean Connery in two.

As it happens, by far the majority of uses of lasers would not involve such dramatic activities, but there is no doubt that lasers can pack a punch. So how does a beam of insubstantial light manage to cut through gold and slice up spies? It’s worth taking a step back to something most of us have played with as a child – using a lens as a burning glass.

Heat from light

We are used to the feel of sunlight’s warmth on our skins. One of the forgotten senses, when we claim there are five, is the way that our skins can detect infrared, light that is just below the visible range in the spectrum. But focus the rays of the Sun with a convex lens and the result is far from a pleasant warmth – in fact there is enough concentrated energy to scorch wood and make paper burst into

flames. Some of the incident photons are re-emitted, enabling us to see the object in the sunlight, but when others excite electrons, the resultant energy goes into vibration in the atoms: it heats them up. By concentrating the light with the lens there is simply too much energy pumped into too small a region. The temperature shoots up to the extent that the material starts to react with the oxygen in the air in the chemical process we call combustion.

The burning glass rarely manages much more than setting a piece of paper alight, although house fires are sometimes caused by glass vases focusing the Sun’s rays and starting a blaze. But way back in Ancient Greek times, the mathematician and engineer Archimedes proposed an optical defence mechanism for his city. In danger of attack by Roman vessels, he suggested that huge curved mirrors be constructed on the harbour. These would be used to concentrate the rays of the Sun, setting the attacking ships alight. The principle might well have worked had the ships been still enough, especially if tar had been used to seal gaps in the wood, though as far as we aware the mirrors were never constructed. In principle, though, here was the first death ray.

A laser cuts on exactly the same principle as a burning glass, but with the difference that the light is far more concentrated, even at a considerable distance, and the waves (or phase of the photons) are in step, making the impact more likely to transfer energy to the target efficiently.

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