Текст 1. Physics. Period III (from 1970 to the end of the 20th century)

Physics. Period III (from 1970 to the end of the 20th century)

Basic and applied science are interwoven; they are like a tree whose loots correspond to basic science. If the roots are cut, the tree will degenerate.

Another intellectual value is the role that basic science plays in the education of young scientists. It fosters a kind of attitude that will be most productive in whatever work the students will finally end up with. Experience has shown that training in basic science often produces the best candidates for applied work. Basic science also has ethical values. It fosters a critical spirit, a readiness to admit 'I was wrong', an antidogma attitude that considers all scientific results as tentative, open for improvements or even negation by future developments. It also engenders a closer familiarity with Nature and a deeper understanding of our position and role in the world nearby and far away.

Much too little effort is devoted by scientists to explaining simply and impressively the beauty, depth, and significance of basic science, not only its newest achievements, but also the great insights of the past. This should be done in books, magazine articles, television programmes, and in school education. The view should be counteracted that science is materialistic and destroys ethical value systems, such as religion. On the contrary, the ethical values of science should be emphasized. Final­ly, it would help to point out the positive achievements of applied sci­ence, the contribution to a higher standard of living, and the necessity of more science to solve environmental problems.

It looks as if we are facing a more pragmatic era, concentrating on applied science. Perhaps the end is nearing of the era of one hundred years full of basic discoveries and insights under the impact of the The­ory of Relativity and that of Quantum Mechanics. Even so, we will always need basic research based on the urge to understand more about Nature and ourselves.

Lasers

The story of the laser, a device that produces a powerful beam of very pure light able to slice through metal and pierce diamond, began when physicists were unraveling the secrets of the atom.

In 1913 the Danish physicist Niels Bohr pointed out that atoms can exist in a series of states and each state has a certain energy level. Atoms cannot exist between these states but must jump from one to another. An atom at a low-energy level can absorb energy to reach a high-energy level. When it changes from a high to a low-energy level, it gives out the surplus energy in the form of radiation. If the radiation is given in the form of visible light, the light will all be of the same wavelength (that is, colour). The atom at a high-energy level may emit this radiation spontaneously. Or, as the German-born physicist Albert Einstein pointed out in 1917, it may be triggered into doing so by other radiation. It is on this latter proc­ess, called the stimulated emission of radiation, that the laser depends.

Stimulated emission was not thought useful until the early 1950s, when the physicists C.H. Townes in the United States and N.G. Basov and A.M. Prokhorov in Russia suggested how it could be used to am­plify microwaves - electro-magnetic radiation with very short wave­lengths outside the visible spectrum - and used, for example, in radar.

In 1953 Townes built the first device to amplify microwaves using stimulated emission. He used ammonia gas as the source of high-ener­gy (or 'excited') atoms. Later it was found that a ruby crystal could be used as well. The device became known as the maser, from the initials of 'Microwave Amplification by Stimulated Emission of Radiation'. For their pioneering work on masers Townes, Basov and Prokhorov were jointly awarded the 1964 Nobel Prize for physics.

In 1958 Townes and his brother-in-law, Arthur Schawlow, out­lined a design for an optical maser - that is one producing visible light rather than microwaves. This idea gave birth to the laser - 'Light Am­plification by Stimulated Emission of Radiation'.

Two years later the American physicist Т.Н. Maiman built the first laser, using a cylindrical rod of artificial ruby whose ends had been cut and polished to be exactly flat and parallel. It produced brief, penetrat­ing pulses of pure red light with 10 million times the intensity of sun­light. The pulsed ruby laser is still the most powerful type of laser. The emergent laser beam differs from an ordinary light beam m several respects. Whereas ordinary light is made up of several wave lengths (colours), the laser light consists of a single wavelength. And whereas ordinary light spreads out from its source in all directions, a laser beam is almost perfectly parallel.

The ruby laser was followed, also in 1960, by a gas laser, developed by D.R. Herriott, A. Javan and W.R. Bennett at Bell Telephone Lab oratories in the United States. Gas lasers are not as powerful as rub\ lasers but emit a continuous beam that can be left on like a torch, m contrast to the ruby laser which emits its light in very short pulses.

The purity of wavelength and straight-line beam of lasers have main applications. In industry the heat of the beam is used for cutting, boring and welding. In tunnelling, lasers guide the boring machines on a perfectly straight line; the laser beam remains accurately focused over long distances. Even after travelling a quarter of a million miles from the earth to the moon, a laser beam would have spread only a few miles.

Using the laser in a way similar to radar - sending out a light pulse and timing when its reflection ('echo') returns - provides a very accu­rate method of distance measurement in space as well as on earth. By this means the distance to the moon at any time can be calculated to the nearest foot. Lasers are used in telecommunications by FIBRE OPTICS, and create three-dimensional photographic images in HOLOGRAPHY.

In medicine, lasers are used in eye surgery to weld back in place a detached retina - the light-sensitive screen at the rear of the eye-ball. The heat of a ruby laser pulse causes a 'burn' which, in healing, devel­ops scar tissue that mends the tear. Lasers can be used to treat glauco­ma, a condition in which pressure builds up in the eye-ball. The laser punches a tiny hole in the iris to relieve the pressure, the patient feeliny no more than a pinprick. Laser scalpels are also coming into use. They make a fine incision and at the same time cauterise (heat seal) the blood vessels, reducing bleeding.

Lasers are applied in art as well. It is possible to mention the fa­mous concert with laser effects of J.M. Jarrenear Egyptian pyramids at the beginning of the 3rd millennium.