At this point, the second atom also emits light. The two flashes of light travel on their path together, both in exactly the same direction. This process is known as stimulated emission. A little bit further on they might collide with two atoms which in turn emit two additional flashes of light. In this way, the intensity of light is doubled with every subsequent collision.
All light waves run precisely in phase with each other and are of the same colour.
All together this produces a particularly powerful, bright beam of light. That is the great difference between the light from a laser and an incandescent lamp. The light produced by a filament shines in different directions and is all colours of the rainbow. The light from a laser is therefore much more concentrated. This makes the laser light very suitable for shining light on microscopically small structures on a video disc.