You can also use "láseres", it's also common use, but more for "variety", than for "plural of ray". You can see Rusty's examples.
So if you want to speak of variety use "láseres"
"hay una gran cantidad de láseres disponibles"
"se puede elegir entre distintos láseres..."
If you want to sepak of "plural of beam " then "rayos láser"
"tras emitir una descarga de rayos láser, se destruye la célula"
This is my usage, you can say it otherwise.
saludos
