Intense light beam (5)
I believe the answer is:
laser
'intense light beam' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for laser that I've seen before include "Light-gun" , "Device producing an intense light beam - kind of sailing dinghy" , "Intense light generator" , "Powerful light source" , "Device producing an intense beam of light or radiation" .)