At its most basic, a laser is a light source. To understand how it can become a weapon, it's helpful to think about how it's different from the light sources that are around you every day. Start with an ordinary incandescent light bulb. The bulb sends light waves out in every direction. These waves, just like waves in water, have peaks and troughs, or high points and low points. If you were able to see each light wave coming from an incandescent bulb, you'd see lots of peaks and troughs passing you at the same time. There are also lots of frequencies, or colors, of light coming from a light bulb, and they all combine to create what looks like white light.
Now, think of a flashlight. A flashlight's beam is more focused than what comes from a naked light bulb. Most of its light travels in one direction, depending on where you point the flashlight. There are still lots of frequencies of light that combine to create white light, and the peaks and troughs of the different light waves pass by at different times.
A laser is even more focused than a flashlight. It creates only one wavelength, or color, of light. The peaks and troughs from the light waves are also synchronized peak to peak and trough to trough. This means that the different waves don't interfere with each other. This light travels only in one direction. The light beam can be tightly focused and remain so over great distances. Lasers can produce light of tremendous powers (1,000 to 1 million times stronger than a typical light bulb). Various types of lasers can produce various wavelengths of light, from the infrared range through the visible wavelengths to the ultraviolet range.
Light is basically moving energy. A laser produces very intense energy that can travel over very long distances. That's why a laser can become a weapon while the light from an incandescent bulb typically can't.
To do this, a laser has to produce light in a nonconventional way. "Laser" stands for light amplification by stimulated emission of radiation. In other words, a laser produces light by stimulating the release of photons, or light particles. A laser needs four basic parts to do this:
- Lasing medium: a source of atoms that get excited and emit light of a specific wavelength. The medium can be a gas, liquid or solid.
- Energy source: primes or pumps the atoms in the lasing medium to an excited state
- Mirrors: a full mirror and a half-silvered mirror. The mirrors allow the emitted light to bounce back and forth within the lasing medium cavity and ultimately to escape to the outside
- Lens: most lasers have some type of lens to focus the beam.
The lasing process is all about storing and releasing energy. An energy source injects energy into the lasing medium. The energy excites electrons, which move up to higher energy levels. When the electrons relax, they emit photons. The photons move back and forth between the mirrors, exciting other electrons as they go. This produces powerful, focused light.
Next, we'll start to look at some of the lasers being used for the military.