The ~laser~ is a coherent beam of light, used in the laser printer to electrostatically charge the photosensitive surface of the printer drum. The lasers can be solid state or gas phase, depending upon the speed and resolution desired. Faster laser printers, which have greater resolution, require a gas laser. Simpler printers commonly use a solid state laser diode. A complex array of collimating and focusing lenses is required to direct the laser beam precisely along the printer drum's surface.
