A new technique to control laser intensity

A new technique to control laser intensity TWO PHYSICISTS in Hyderabad studying the properties of light have devised a way to expand the range of intensity of laser beams.

G S Agarwal and S P Tewari, both from the University of Hyderabad, are working on methods to produce laser radiation of a desired intensity using the concept of exposing atoms to electromagnetic radiation.

Lasers are widely used as light sources in physics as they have many desirable properties. A laser beam has the same relationship to light from an ordinary electric bulb as a platoon of soldiers, marching exactly in step has to a jostling, disorderly mob.

But for all their numerous advantages, lasers have one major limitation -- they can be produced at certain frequencies only. "Increasing the number of frequencies on which laser beams can be produced would be a great boost to experimental work," says Tewari, who together with Agrawal, has developed just such a technique.

The frequency of light produced by a laser depends on the atomic system of the medium used, which can be a gas such as nitrogen or carbon-dioxide. When energy is pumped into the medium from an external source, several atoms in the medium are excited to higher energy levels. When these excited atoms are induced to return to the lower energy level, they cause energy to be emitted in the form of light.

Agarwal and Tewari have shown that by exposing an atomic system to electromagnetic radiation, atom movement from one energy level to another can be controlled. In this way, the lasers can be produced at required frequencies. This result, first predicted by Agarwal and Tewari, has been verified in experiments performed by a group of physicists in the US.

Agrawal and Tewari are now extending their results to a wider range of atomic systems. "Our eventual aim is to be able to produce laser radiation of any required frequency in the lab by applying suitable electromagnetic fields to a small set of atomic systems," says Tewari.

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