The laser head is composed of a light-emitting tube, condenser lens and adjustable copper sleeve and it is assembled when delivered, the focal length of the lens is adjusted glued by strong glue stick, which can work directly after connecting to a 5V DC power supply. Pay attention to the laser cell to prevent from being burnt or battery explosion due to a short circuit when removing the battery. The principle of laser emission and the specificity of generation process determines the characteristics of laser which common light do not have: nice monochromaticity, coherence and directionality and high brightness. It is mainly used in laser toys, all kinds of level meters, laser projector, etc.