Laser Safety: Everyday Life in a New Light

by Food and Drug Administration (FDA)

Every spring, high school science teacher Robert Donaldson pulls out equipment he knows will fascinate the juniors and seniors in his optics class. Using a low-powered laser beam, he demonstrates the properties of light: how it reflects, bends, and travels through objects.

The teenagers, students in an accelerated science program at Montgomery Blair High School in Silver Spring, Md., eagerly wait their turn to experiment with one of several lasers in the classroom.

"This is something they've heard about for most of their schooling," says Donaldson. "They've seen pictures, they watched 'Star Wars.' They love to get their hands on them."

Light is as old as the stars, but the kind of light Donaldson uses in class — laser light — is a relative newcomer under the sun.

Developed just over 30 years ago, lasers have revolutionized industry, medicine and science. They play our compact discs. They can carry our phone messages. They entertain us with light shows in the night sky. They are powerful enough to cut through an inch of steel and precise enough to drill 200 holes in the head of a pin.

Perhaps lasers are best known for their feats in medicine. Doctors use them to vaporize or mend tissue with minimal scarring or swelling.

Lesser known, however, are the hundreds of ways in which non-medical lasers affect our lives every day. Like medical lasers, these are regulated by FDA for safety. Non-medical lasers are in the grocery store, the office, our schools, and even our homes.

"They've reached that point where they're everywhere. You can't get away from them," says Peter Baker, executive director of the Laser Institute of America in Orlando, Fla.

"The old saying was that lasers were a solution looking for a problem," Baker adds. "In the early years, they tended to be a bit exotic and unreliable. You had to have a Ph.D. to know how to keep them tweaked up and reliable."

Today, however, lasers are dependable enough to be useful in a wealth of technologies. They're not just for Ph.D.s anymore.

What Is a Laser?

Laser is an acronym for "light amplification by stimulated emission of radiation." Radiation, in this case, is another word for electromagnetic energy, which includes light.

Laser light has several properties that make it different from regular light. First, it is often collimated, which means it travels in a narrow beam for long distances, rather than going off in many directions as regular light does.

Laser light is also coherent, which means that the light waves stay synchronized over long distances. And it is monochromatic, of one color. Some laser beams are invisible, producing light in the infrared or ultraviolet wavelengths.

A laser can produce a short burst of light or a continuous beam. Because it can focus narrowly, laser light can be much more intense than regular light, especially in bursts. Laser beams range in power from a few microwatts to several billion watts in short bursts.

How a Laser Works

To understand how a laser works, first you have to understand something about light.

Light is the visible form of electromagnetic energy. Some electromagnetic energy cannot be seen, but it is everywhere in the universe. It is made of tiny energy packets, called photons, traveling in a stream of wave patterns, called electromagnetic waves.

All objects emit electromagnetic energy in varying wavelengths and directions. Photons are emitted when atoms spontaneously change from one energy state to another. We can feel some of them as heat, and we can see others as light. But even when we can't see or feel them, photons are moving all around us in different directions, getting absorbed by atoms and released again.

In a laser, however, the photons are emitted in the same general wavelength and direction.

It was Albert Einstein who first conceived of laser light. In 1917, he theorized that atoms could be stimulated to release energy with a specific wavelength and direction. But it wasn't until 1960 that Theodore Maiman, an American scientist, put together the first successful laser.

Like Maiman's invention, many lasers today contain three major parts. First, there's a cylinder-shaped rod called the lasing medium. Maiman used a synthetic crystal ruby, but today's lasing mediums are often glass tubes filled with liquid or gases such as helium, neon, argon, and carbon dioxide.

Second, a laser has a power supply that excites the atoms in the lasing medium with energy. The power supply charges the atoms to their capacity, eventually causing them to release photons in one wavelength and direction.

The third part of a laser is a set of mirrors, one on each end of the lasing tube. As the atoms release photons, the mirrors reflect them back and forth. With each pass through the lasing medium, the energy is amplified. One of the mirrors reflects only part of the light, so some of the photons escape through the end of the tube as a narrow laser beam.

There are a number of variations to lasers. Chemical lasers, for example, get their energy from chemical reactions instead of electricity. Lasers filled with liquid dye use complex molecules to produce more than one wavelength. And semiconductor diode lasers, some of which are smaller than a grain of salt, are made from circuitry similar to the light-emitting diodes in digital watches and calculators. These lasers emit tiny beams of coherent light.

Today, laser production is a billion-dollar industry worldwide, according to Laser Focus World magazine. Manufacturers, who began by replacing one or two drills with lasers, now design the whole of their manufacturing techniques around them. Some industries have even redesigned their products to be more accessible to laser manufacturing.

Communications and Information Storage

By far the most common lasers are those that transmit and store information. These are the lasers inside compact disc players, laser printers, supermarket scanners, and fiber-optic cables used in telephone lines. Most of the time, these technologies use tiny semiconductor lasers.

Telephone companies convert sound to electrical pulses, then convert the pulses to laser light that can travel through fiber-optic cables. This is more efficient than traditional phone technology, which sends calls over copper wires. With a laser that pulses very quickly, one glass fiber the width of a human hair can transmit the calls of more than 20,000 wires.

Lasers can also record and reproduce music on compact discs. The sound is recorded by a laser beam that burns a pattern of dots into a disc. A tiny semiconductor laser in a compact disc player reads the dots and converts them back to sound. Since only light touches the disc, a CD player gives very clean, clear sound, without the background noise from scratches and dust that you hear on records.

Compact discs are quickly replacing other kinds of recordings, and not just for home stereos. Libraries use them to store data bases, encyclopedias, and other information to access by computer.

What if you need to print out that information? A laser printer can do it quickly in type that looks professionally printed. Inside the printer, a scanning laser moves across a light-sensitive drum. The drum attracts ink where the laser has hit it and transfers the ink to the paper as it rolls by.

A scanning laser can read as well as write. Many grocery and department stores tag their merchandise with Universal Product Codes, labels with striped patterns. Low-powered lasers can "read" the stripes and signal the store's computer to deduct the product from inventory and ring up the price.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.