Laser has many features: first, the laser is monochrome, or single frequency. Some lasers can produce different frequency at the same time, but the laser is isolated from each other, when used is separated. Second, the laser is coherent light. Coherent light is characterized by all of its light waves are synchronized, the beam of light like a "wave train". Again, the laser is highly concentrated, that is to say, it have to walk a long distance will be scattered or convergence phenomenon.