Beam of light (5)
'beam of light' is the definition.
(synonyms)
This is all the clue.
(Other definitions for ray that I've seen before include "may be electric" , "Pencil of light" , "Flat fish or sun beam" , "beamer?" , "Shaft of light" .)
(Other definitions for laser that I've seen before include "Device producing thin beam of light" , "Device that generates an intense ray of light" , "modern light industry" , "Powerful light source" , "Scientific apparatus" .)