I doubt that the word usage preceded the invention of a functioning laser but I think that is possible since the principle of the laser was understood years before one was created.
"Ray guns" I recall seeing in old (1930s) Flash Gordon episodes. "Death rays" were seriously discussed in the 1930s and I believe resulted in radar. I know that of course War of the Worlds had heat rays and Archimedes it appears could have created one long ago (I wonder why if it really worked why people gave up -- maybe you need to live near the equator for such a weapon to work well enough). So any mention of "death" or "heat" rays does not count -- I am looking for "laser" or possibly "maser". What would be really exciting is an old story that discussed the principle upon which lasers and masers are based if that story predates their creation and even more exciting would be if the science fiction story actually is why we use the word laser. I have to say, it is one of the best-sounding acronyms -- the word somehow really seems to suggest what lasers actually are but of course the device and word already existed by the time I learned to speak and so that affects my perception of how apt it sounds.
NOTE: It seems to me that, along with manned spaceflight and the a-bomb, the laser is one of the first "science fiction" technologies that became real.