William T. Silfvast
School of Optics/CREOL
University of Central Florida
Orlando, Florida

Lasers are devices that amplify or increase the intensity of light to produce a highly directional, high-intensity beam that typically has a very pure frequency or wavelength. They come in sizes ranging from approximately one-tenth the diameter of a human hair to that of a very large building. Lasers produce powers ranging from nanowatts to a billion trillion watts (10²¹ W) for very short bursts. They produce wavelengths or frequencies ranging from the microwave region and infrared to the visible, ultraviolet, vacuum ultraviolet, and into the soft-X-ray spectral regions. They generate the shortest bursts of light that man has yet produced, or approximately five million-billionths of a second (5 × 10^–15 sec).

Lasers are a primary component of some of our most modern communication systems and are the probes that generate the audio signals from our compact disk players. They are used for cutting, heat treating, cleaning, and removing materials in both the industrial and medical worlds. They are the targeting element of laser-guided bombs and are the optical source in both supermarket checkout scanners and tools (steppers) that print our microchips.

Because of the special stimulated nature of the laser light source, and the apparatus needed to produce laser light, laser photons are generally not as cheap to produce or to operate as are other light sources of comparable power. We presently do not use them to light our rooms, as lamp bulbs for our flashlights, as headlights for our automobiles, or as street lamps. Lasers also don’t generally provide “white light” but instead produce a specific “color” or wavelength, depending upon the laser used.

The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Stimulated emission of radiation is a natural process first identified by Einstein. It occurs when a beam of light passes through a specially prepared medium and initiates or stimulates the atoms within that medium to emit light in exactly the same direction and exactly at the same wavelength as that of the original beam. A typical laser device (Figure 5-1) consists of an amplifying or gain medium, a pumping source to input energy into the device, and an optical cavity or mirror arrangement that reflects the beam of light back and forth through the gain medium for further amplification. A useful laser beam is obtained by allowing a small portion of the light to escape by passing through one of the mirrors that is partially transmitting.

Figure 5-1  Basic laser components including gain medium, pumping source, and mirror cavity