ABOUT THIS CHAPTER

In Chapter 2, we learned the basic physics and optics needed to understand how lasers work. In this chapter, we will learn what goes on inside lasers-how they are energized and how they produce beams. Here we will learn about the general principles of laser operation; Chapter 4 will describe the important characteristics of lasers.

3.1 BUILDING A LASER

The best way to understand how a laser works is to build one. In this book, we can only build a laser on paper, but we can follow the path of the original developers of lasers. They sat down, sketched out what needed to be done to make their idea work, then figured out how to proceed before they started building anything.

We have the obvious advantage that we know where we are going. Hindsight is always 20-20, so we do not have to pursue all the dead ends that wasted the original developers' time and energy, but reproducing the key steps will help us understand how the pieces go together. Each step is a separate section of this chapter.

The first step toward our conceptual laser is figuring how to produce the population inversion needed for stimulated emission, covered in Section 3.2.

Once we have the population inversion needed for stimulated emission to dominate, Section 3.3 describes how a resonant cavity helps amplify the light enough to make an oscillator.

Then Section 3.4 considers how oscillation creates resonant conditions and generates a laser beam.

Section 3.5 tells how the resonator and laser medium combine to select a laser wavelength.

Finally, Section 3.6 goes back and looks more closely at exciting the laser medium to produce a population inversion.

To keep the discussion simple, we will talk about atomic states rather than molecular states, but remember that the same principles apply to molecules.