Laser printers have become another familiar laser-based consumer product, often used in conjunction with personal computers. Their principle of operation involves electrophotography, also called xerography, the same process that is used in photocopy machines.
The electrophotographic process is illustrated in Figure 24-17. A photoreceptive surface, containing a layer of photoconductive material, is charged uniformly by ions from a corona discharge. The surface is often the surface of a rotating drum. After the charging step, the surface is exposed by scanning the laser beam across it. The intensity of the beam is varied to produce a replica of the image that is desired. The pattern of light intensity reproduces the pattern of the text or graphics that is to be printed. The photoconductive layer becomes conducting in regions illuminated by the laser. This allows the electrostatic charge to move and creates a replica of the pattern in electric charge on the surface.