laser A laser (acronym for light amplification by the stimulated emission of radiation) is a light source that emits photons of the same characteristics in a coherent beam. A laser uses a solid, liquid or gaseous lasing medium, that contains molecules, of which some atoms have electrons that emit photons of the same frequency when falling back to their normal orbital after excitation (pumping) by external means A laser is the most common way to irradiate a cell in a flow cytometer. A laser is the most common way to irradiate a cell in a flow cytometer. Daniel Schober John Quinn http://en.wikipedia.org/wiki/Laser laser light amplification by the stimulated emission of radiation light source metadata incomplete