Lasers

Last updated: December 7, 2009.

Lasers are amazing light beams powerful enough to zoom miles into the sky or cut through lumps of metal. Once the stuff of science fiction, they have proved themselves to be among the most versatile inventions of modern times. The miniaturized laser beam that reads music in a CD player can also guide missiles, send emails down fiber-optic telephone lines, and barcode scan goods at the supermarket checkout.

The basic idea of a laser is simple. It's a tube that concentrates light over and over again until it emerges in a really powerful beam. But how does this happen, exactly? What's going on inside a laser? Let's take a closer look!

Photo: Lasers used in a NASA experiment. Picture courtesy of Great Images in NASA.

How is laser light different from ordinary light?

Lasers are more than just powerful flashlights. The difference between ordinary light and laser light is like the difference between ripples in your bathtub and huge waves on the sea. You've probably noticed that if you move your hands back and forth in the bathtub you can make quite strong waves. If you keep moving your hands in step with the waves you make, the waves get bigger and bigger. Imagine doing this a few million times in the open ocean. Before long, you'd have mountainous waves towering over your head!

Photo: It's much easier to make laser light follow precise paths, as in this experiment to develop better solar cells. Picture by Warren Gretz courtesy of US DOE/NREL (Department of Energy/National Renewable Energy Laboratory).

A laser does something similar with light waves. It starts off with weak light and keeps adding more and more energy so the light waves become ever more concentrated. The "white" light produced by an ordinary flashlight contains many different light rays of different wavelengths that are incoherent (out of step with one another). But in a laser, all the light rays have the same wavelength and they are coherent (in step). This is what makes laser light such a powerful concentration of energy.

Before you can understand how a laser works, you need to know how an atom can give off light. If you're not sure how this happens, take a look at the box how atoms make light in our introductory article about light.

What do we use lasers for?

Cutting tools

Lasers produce such intense and precisely focused energy that they can cut through metals, ceramics, plastics, and cloths. They have become popular in many industrial operations because high-precision computer-controlled lasers are much more accurate than human-operated cutting tools and, unlike traditional tools, laser beams never become blunt. A typical application involves simultaneously cutting hundreds of thicknesses of cloth according to a preprogrammed garment pattern.

Eye surgery

The pinpoint precision of lasers makes them particularly suitable for "welding" detached retinas and sealing broken blood vessels in the eye. The procedure is painless because the laser light passes straight through the patient's eyeball. Laser surgery can also help to correct eye problems such as short sight. Read more in our main article on laser eye surgery.

Scientific research

Since the laser was patented in 1958, lasers have become smaller, more precise, and more powerful. At Lawrence Livermore National Laboratory in California, scientists are currently working to produce the world's most powerful laser, the National Ignition Facility (NIF), for nuclear research. Costing $1.2 billion, it will be able to generate temperatures of up to 100,000,000 degrees.

What other kinds of lasers are there?

The tiny laser beams used in small electronic devices such as CD players work a bit differently. Read all about them in our article on semiconductor lasers.