Printing may be carried out using a LightJet or similar process which uses modulated red, green and blue laser beams (channels) to directly expose the photographic paper. The laser beams are often controlled (modulated) individually from one another using their own acousto-optical modulator (AOM) crystal, each of which is driven by its own AOM driver. The AOM driver can often fail causing problems in the image produced by the printing process. Many minilabs use DPSS lasers while others use laser diodes to generate the laser beams, or may use both. The printer may also print information onto the back of the paper for identification. Alternatively the laser beams may be modulated directly by varying the power sent to the laser diodes. Often the green and blue lasers are DPSS lasers. Lenses, diaphragms and