Intense beam (5)
I believe the answer is:
laser
'intense beam' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for laser that I've seen before include "E.g. surgical light-beam" , "Device that generates an intense ray of light" , "Device that produces an intense beam of light" , "light-intensifier" , "Source of light; type of printer" .)