Intense beam of light (5)
I believe the answer is:
laser
'intense beam of light' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for laser that I've seen before include "Device producing an intense light beam - kind of sailing dinghy" , "E.g. surgical light-beam" , "Device producing thin beam of light" , "Scientific apparatus" , "Optical device producing an intense beam of light" .)