ENGLISH ( counterble and uncounterble nouns )

Lasers, once imaginary death rays in science-fiction comic, are now saving life. These powerful beams of light(no s because beams already has an s) are being used by doctor to destroy cancer cells. The lasers literally vaporize their targets. The health(no s) of patient is ensured, as there are no side-effect. Lasers have a number of applications beyond medicine too. At some supermarkets till laser are used to read bar codes on item, (what did they use before laser, e.g. manpower ?). The military uses laser to guide missile to their target. Lasers are also used in factory to cut through glass, metal and even clothing. Compact disc player also work by using laser. They pick up laser light reflected in pulses from the surface(no s) of the disc.