Since the first laser was demonstrated in 1960, lasers have become useful in many areas of human endeavour, from medicine to manufacturing to music recording. Laser-based systems transmit intercontinental telephone conversations, or detect trace amounts of toxic gases in the atmosphere, as well as probing the deepest secrets of chemical reactions at the molecular level. Such versatility has led many scientists and engineers to work on the design, understanding and applications of lasers in the past few decades, and the pace of development is still rapid.
Lasers produce light, just as an incandescent light bulb does.
However, the light emitted from a laser has certain characteristics which make it valuable in many applications. It is coherent, directed and monochromatic. These characteristics mean that it can be focussed tightly to a small spot, or allowed to propagate over a long distance, such as to the moon and back. Laser light can also be concentrated in short pulses with high peak power, or can operate continuously. In this chapter, we will describe how a laser works, and discuss some of the historically and practically important lasers which have been developed.