What is a laser? The word laser is short for light amplification by stimulated

emission of radiation. Laser light is an entirely new kind of light, more brilliant,

more intense than anything found in nature. Laser light can be so powerful that it

can vaporize any known material on earth in a fraction of a second. It can bore

holes in the toughest metals or easily pierce the hardness of a diamond.

In contrast, less powerful, exquisitely precise beams from other kinds of

lasers can be used to perform extremely delicate operations, such as surgery on

the human eye. Laser light can be controlled very exactly and can be produced in

a steady beam called a continuos wave or in a rapid-fire, bursts of light called

pulses.
Although the underlying principles of lasers had been know for over 40

years, the demonstration of the first laser opened the floodgates to one of the

most exciting and far-reaching technilogical developments of the 20th century.

Within a few years of the first laser demonstration, many different kinds of lasers

were being used a practical tools in a variety of ways. And, as we shall see, lasers

have brought about truly revolutionary new technologies that will continue to

affect our lives in the future.
Today, a broad spectrum of lasers is being used all around us. In

supermarkets and many other large-volume retail stores us lasers to automatically

scan, record prices, and inventory items we buy at the checkout counter. Video

systems use laser light to "read" video disks and produce a moving picture with

an accompanying sound track. Large quantities of information are stored on laser

disks to be read on a computer screen or printed onto paper as a hard copy by a

laser printer.
In medicine, laser light is used as a new kind of bloodless "scalpel" that

seals blood vessels as it cuts through tissue during operations such as the removal

of a diseased gall bladder. Lasers also are making some visits to the dentist less

painful and are used to manufacture dental crowns and bridges.

Lasers are used in industry for heat heating of metals, welding parts together

and precisely aligning equipment. Lasers are used to measure exactly both very

large and small distances. In addition, lasers are teamed with optical fibers for

better data transmission and improved telephone communication. Lasers are

changing the ways scientists do research. And lasers also may create a new source

of electrical power similar to the process our sun uses to produce energy.

How does a laser work? Every laser has certain basic parts. First there must

be an energy source. Often the energy source is electricity, but a strong source of

ordinary light, a chemical reaction, or even another laser can also be used.

Another necessary component of a laser is know as the active medium. The

active medium is a material that can absorb and release energy. It can be a solid,

such as ruby or other crystal, a liquid, such as certain dyes, or a gas, such as

carbon dioxide. The laser beam is actually generated in the active medium.

The final basic part of a laser is the feedback mechanism. The feedback

mechanism consists of two mirrors or other reflective surfaces placed at each end

of the active medium. The mirrors build up the strength of the laser beam. One of

the mirrors, know as the output coupler, is only partially reflective.

Laser action occurs in several steps. The energy source gives off a flash of

light that is absorbed by the active medium. The absorbed energy excites some of

the atoms of the active medium to a higher energy level. Repeated bursts of light

from the energy source may continue to exicite, or pump, the atoms of the active

medium. When there are more excited, high-energy atoms than low-energy atoms

present in the active medium, a population inversion exists. Population inversion is

necessary for laser action to occur.

During laser action, high-energy atoms returning to a low-energy level get rid

of their excess of energy by giving out tiny amounts of light called photons. This

light, in turn, excites other atoms in active medium to release light as well. In this

way, a chain reacation of growing energy cascades through the active medium.

More and more atoms in the active medium