397. What is an interference pattern in lasers?
When the wave of light emitted by a laser can follow more than one path to a target, the waves taking the different paths may "interfere" with one another. If the electric field in the wave taking one path is in phase with (always pointing in the same direction as) the wave taking another path, then the two waves will help one another and they will push together on charges in the target. The amount of light reaching the target will be particularly strong. However, if the two waves arrive out of phase with one another (always pointing in opposite directions), then they will cancel one another and the amount of light reaching the target will be particularly weak. Usually a pattern of bright and dark regions appears on an extended target as the waves following different paths alternately interfere constructively (helping one another) and destructively (canceling one another).