A laser generates a beam of very intense light. Laser light has three distinct characteristics that distinguish it from ordinary light: Laser light is:
A laser beam is collimated, meaning it consists of waves traveling parallel to each other in a single direction with very little divergence (Figure 1).
This allows laser light to be focused to very high intensity (Figure 2). Ordinary light waves spread and lose intensity quickly.
Monochromatic refers to the single (wavelength) color of a laser beam. Ordinary white light is a mixture of colors, as you can demonstrate by shining sunlight through a prism. Because the wavelength of laser light determines its effect on tissue, the monochromatic property of laser light allows energy to be delivered to specific tissues in specific ways.(Figure 3).
Laser light is coherent, which means all the light waves move in phase together in both time and space. A laser has a very tight beam that is strong and concentrated. A flashlight, by comparison, releases light in many directions; the light is weak and diffuse.