An Overview of Laser Technology

The word laser is an acronym that stands for "light amplification by stimulated emission of radiation." In a fairly unsophisticated sense, a laser is nothing more than a special flashlight. Energy goes in, usually in the form of electricity, and light comes out. But the light emitted from a laser differs from that from a flashlight, and the differences are worth discussing. You might think that the biggest difference is that lasers are more power- ful than flashlights, but this conception is more often wrong than right. True, some lasers are enormously powerful, but many are much weaker than even the smallest flashlight. So power alone is not a distinguishing characteristic of laser light.
Now it'senough to say that there are three differences between light from a laser and light from a flashlight. First, the laserbeam is much narrower than a flashlight beam. Second, the white light of a flashlight beam contains many different colors of light, while the beam from a laser contains only one, pure color. Third, all the light waves in a laserbeam are aligned with each other, while the light waves from a flashlight are arranged randomly. The significance of this differ- ence will become apparent as you read through the next several chapters about the nature of light.

Lasers come in all sizes—from tiny diode lasers small enough to fit in the eye of a needle to huge military and research lasers that fill a three-story building. And different lasers can produce many different colors of light. As we explain in Chapter 2, the color of light depends on the length of its waves. Listed in Table 1.1 are some of the important commercial lasers. The "light" produced by carbon dioxide lasers and neodymium lasers can- not be seen by the human eye because it is in the infrared portion of the spectrum. Red light from a ruby or helium-neon laser, and green and blue light from an argon laser, can be seen by the human eye. But the krypton-fluoride laser's output at 248 nm is in the ultraviolet range and cannot be directly detected visually. Interestingly, few of these lasers produce even as much power as an ordinary 100-W lightbulb. What's more, lasers are not even very efficient. To produce 1W of light, most of the lasers 1 would require hundreds or thousands of watts of electricity. What makes lasers worthwhile for many applications, however, is the narrow beam they produce. Even a fraction of a watt, crammed into a supernarrow beam, can do things no lightbulb could ever do.

The ruby, yttrium aluminum garnet (YAG), and glass lasers listed are solid-state lasers. The light is generated in a solid, crystalline rod that looks much like a cocktail swizzlestick. All the other lasers listed are gas lasers, which generate light in a gaseous medium like a neon sign. If there are solid- state lasers and gaseous lasers, it's logical to ask if there's such a thing as a liquid laser. The answer is yes. The most common example is the organic dye laser, in which dye dissolved in a liquid produces the laser light.