The word laser had a name before the thing worked, and a notary before it had a patent.
It is an acronym: light amplification by stimulated emission of radiation. It copies an older acronym, maser, which Etymonline dates to 1955 and which stands for microwave amplification by stimulated emission of radiation. A maser amplified microwaves. The next goal was to do the same with visible light, and early researchers simply called such a device an "optical maser."
Gordon Gould, then a doctoral student at Columbia, gave it a shorter name. In November 1957 he filled a notebook with calculations under the heading "Some rough calculations on the feasibility of a LASER: Light Amplification by Stimulated Emission of Radiation." Wikipedia calls this the first recorded use of the term. Charles Townes, a maser pioneer, had advised him to get his notes notarized. Electronic Design reports that Gould took the notebook to a local candy store to be stamped.
Gould first used the acronym in public in a 1959 conference presentation. In April 1959 he also filed patent applications. Townes and Arthur Schawlow had applied in 1958, and their patent was granted in March 1960. Gould spent about thirty years in court. His first key patent came in 1977. Electronic Design says that by 1988 his amplifier patents covered 80 percent of the lasers made in the United States.
The device caught up with the word on May 16, 1960. Theodore Maiman ran the first working laser at Hughes Research Laboratories, using a ruby crystal to make pulses of red light. Etymonline dates the word "laser" to that year.
Physicists like to point out the name is slightly off. A laser makes its own light, so it is really an oscillator, not an amplifier. Wikipedia notes that "loser," for light oscillation by stimulated emission of radiation, would have been more accurate. Nobody chose that version.
The acronym has since behaved like an ordinary word. It lost its capital letters, and by 1962 it had produced a verb: a working laser is said to "lase."