88 Lasers-High

Lasers FOCUS Question How do the properties of lasers make them useful?

What Are Lasers? A doctor carefully seals off leaking blood vessels during surgery. A machine slices through many layers of fabric at once. A metalworker lines up two steel panels and bonds them securely together. All this work is done using lasers. A laser is a narrow, concentrated beam of light. Laser beams do not occur naturally on Earth. The lasers we see around us are the products of human ingenuity. They have unique properties that allow them to be used in a variety of ways. Word Wise An acronym is a word that is an abbreviation made from the first letters of other words. The word laser is an acronym that stands for Light Amplification (by) Stimulated Emission (of) Radiation.

In Perfect Sync How does a laser beam differ from a flashlight's beam? Remember, light can travel in waves. A flashlight emits the full range of visible light waves, from red to violet. These colors have different wavelengths— the distance from peak to peak in a wave. When these different wavelengths travel together, they blend and produce a broad beam of white light that spreads and fades as it moves outward. By contrast, lasers produce light waves with the same wavelength that together make a single-colored, or monochromatic, beam of light. The light waves are synchronized perfectly. They form a highly focused beam of light that can travel a great distance without fading.

Making a Laser Beam Creating a laser beam is exciting— literally. A medium— a substance that is usually a gas— is placed in a chamber called a resonator. The chamber has mirrors on opposite sides. A burst of electrical energy passes through the medium. The energy causes the electrons in the medium's atoms to become excited and move faster. When the energy is removed, the electrons slow down. As they do, they release light particles called photons. Energy is switched on and off very quickly to make the electrons speed up and slow down many times. The electrons keep producing photons as they change speed.

The photons collect in the chamber, bouncing back and forth between the mirrors and moving even faster. Eventually, a stream of photons shoots out from the chamber through one of the mirrors. Scientists presented the scientific theories that are the basis of laser technology in the early 1900s. At first, they had little idea of how lasers might be useful. It wasn't until 1960 that the first laser was constructed. By 1961, a medical laser was used at a hospital in New York City to destroy an eye tumor. From that point on, the use of lasers grew, not just in medicine but also in other fields.

Cutting-Edge Technology Lasers are pure light energy. A laser beam by itself is not hot. It can generate heat, however, if it hits a material that can readily absorb its light energy. The beam's sharp focus creates a point with enough heat to vaporize, or remove, the material in that spot. This property makes a laser beam a useful cutting tool. In medicine, lasers are especially useful as surgical instruments. They can get to hard-to- reach places better than other cutting tools. Tumors that are otherwise inoperable can be burned away. Because it is easy to direct the laser, doctors can avoid damaging healthy tissue. Lasers are often used in delicate operations on eyes. Safety! Lasers can hurt as well as help eyes. A laser beam raises the temperature of the surface it hits. Laser pointers aimed at the eyes can cause temporary or even permanent loss of vision.