ABOUT THIS CHAPTER

This chapter will introduce you to lasers. It will give you a basic idea of their use, their operation, and their important properties. This basic understanding will serve as a foundation for the more detailed descriptions of lasers and their operation in later chapters.

1.1 THE IDEA OF THE LASER

Optics was a sleepy backwater of physics when Theodore Maiman demonstrated the first laser in 1960. His announcement made headlines, and for many years afterward, lasers were novelties that attracted attention. Today, lasers are commonplace in developed countries. Thanks in large part to the laser, optics has become a dynamic field, expanding far beyond the binoculars, cameras, and spectacles that were the main products of the optical industry half a century ago.

We take lasers almost for granted today, as just another wonder of our technological age along with satellites and electronic chips. Most of us think of lasers as cylindrical devices that emit pencil-thin beams of red or green light, and shine bright spots on the wall. The first kind of laser to come to your mind is likely to be the pen-like laser pointers you can buy for $10 or less at an electronics or stationary store.

But lasers come in many other sizes, shapes, and forms. Most of them are tiny semiconductor chips that we never see because they are hidden inside electronic equipment such as CD players, CD-ROM drives, and DVD, or Blu-Ray players. Others are tubes filled with gas that emit laser light. Some are boxes the size of a filing cabinet or a refrigerator that emit powerful beams to cut or drill holes in metal or plastic. The largest lasers fill the interior of a building and generate pulses of light that for a fleeting billionth or trillionth of a second can deliver more power than the whole U.S. electric power grid. Laser output may not be visible; many lasers emit at infrared or ultraviolet wavelengths invisible to the human eye.

What makes them all lasers is that they generate light in the same way, by a process called "light amplification by the stimulated emission of radiation." The word "LASER" is an acronym for that phrase. It is the process of amplifying stimulated emission that makes laser light special. The sun, light bulbs, flames, and other light sources emit light in a different way, spontaneously. That leads to important differences between laser light and other kinds of light, which we will explain later.

Most of us also are familiar with fictional weapons that resemble lasers and sometimes are called lasers. The deadly heat rays used by the Martian invaders of Earth in The War of the Worlds seem uncannily like lasers, emitting beams of invisible infrared light. Yet H. G. Wells wrote the book in 1896, long before anyone had thought of stimulated emission or lasers. Wells just imagined a searchlight beam that could burn rather than illuminate.

Pulp science fiction writers soon churned out tales of ray guns or death rays, which fired deadly beams of light or other (often undefined) forms of radiation. The writers may have heard rumors that legendary inventor Nikola Tesla and a handful of other scientists were working on death rays in the 1920s and 1930s, but there was no real science behind their weapons. They were just futuristic props to avoid arming 25th century heroes with six-shooters. But thanks to those stories, when the laser was invented the public thought of it as a "death ray," much to the annoyance of the people working with real lasers.

It is true that military researchers are trying to develop laser weapons. That is not new; it has been going on since the 1960s and so far has consumed many billions of dollars to shoot down a few targets. As you will learn in Section 12.8, laser weapons are big, and they try to destroy targets by focusing a lot of light energy on them. In short, it is not easy to make lasers into weapons. This book is about real lasers, so we will start by looking at the fundamental concepts behind real-world laser technology, briefly explaining what they are and how they developed.