The word ‘laser’ is made up from the initials of the words that describe its action, Light Amplification by Stimulated Emission of Radiation. An American physicist, Theodore H, Maiman, invented and first demonstrated it in 1960.
One of the earliest types of laser was the solid ruby laser, made from a ruby crystal or an artificial ruby rod. The chromium atoms in the ruby are stimulated to emit the laser light. An electronic flash tube coiled round the rod gives out intense bursts of light that excite the chromium atoms from a low-energy to a high-energy state.
After a few thousandths of a second, the atoms revert to their normal state, spontaneously emitting an energy package known as a photon. When a photon strikes another chromium atom still in a high-energy state, it stimulates it to emit an identical photon.
The parts of identical photons travel together in the same direction and exactly in step. The beam is built up by millions of them being reflected back and forth between mirrors at each end of the ruby rod. It finally emerges through a half-silvered mirror at one end, in bursts (pulses) of red light of about one-thousandth of a second.
The laser’s power lies not in the amount of its energy, but in the concentration. The beam is very straight, and the photons – all strike the same surface at the same moment. a laser beam can be powerful enough to burn a hole in a steel plate, or delicate enough to be used in eye surgery.
The smallest lasers now in use are semiconductor lasers. They produce an invisible infrared beam when charged with an electric current.
Picture Credit : Google