LASER is actually an acronym, which stands for light amplification by stimulated emission of radiation. In other words, a laser is a single-wavelength (one color of light) source of high-energy light, which can be accurately focused to transmit that light on to a very small area.
This high-energy beam of light can be used to selectively transfer its energy into tissue to treat the skin. Lasers contain a material that produces and amplifies light. Two mirrors cause the light to reflect back and forth through this material. The result is a light beam that is collimated and intense. This light is either one pure color or several different pure colors. These properties which separate the laser from a light bulb, are important to the medical application of lasers.
There are two basic types of lasers used for cosmetic purposes: Ablative and Nonablative. Ablative lasers actually vaporize the top layers of damaged skin, while Nonablative lasers work deeper in the skin without removing or otherwise damaging the top layers. For this reason, there is no real patient downtime associated with cosmetic procedures that employ solely non-ablative laser technology.