By 1957, many scientists including Townes were looking for a way to achieve maser-like amplification of visible light. In November of that year, Gould realized that one could make an appropriate optical resonator by using two mirrors in the form of a Fabry–Pérot interferometer. Unlike previously considered designs, this approach would produce a narrow, coherent, intense beam. Since the sides of the cavity did not need to be reflective, the gain medium could easily be optically pumped to achieve the necessary population inversion. Gould also considered pumping of the medium by atomic-level collisions, and anticipated many of the potential uses of such a device.
The first page of the notebook in which Gould coined the acronym LASER and described the essential elements for constructing one.
Gould recorded his analysis and suggested applications in a laboratory notebook under the heading "Some rough calculations on the feasibility of a LASER: Light Amplification by Stimulated Emission of Radiation"—the first recorded use of this acronym. Gould's notebook was the first written prescription for making a viable laser and, realizing what he had in hand, he took it to a neighborhood store to have his work notarized. Arthur Schawlow and Charles Townes independently discovered the importance of the Fabry–Pérot cavity—about three months later—and called the resulting proposed device an "optical maser". Gould's name for the device was first introduced to the public in a conference presentation in 1959, and was adopted despite resistance from Schawlow and his colleagues.
Eager to achieve a patent on his invention, and believing incorrectly that he needed to build a working laser to do this, Gould left Columbia without completing his doctoral degree and joined a private research company, TRG (Technical Research Group). He convinced his new employer to support his research, and they obtained funding for the project from the Advanced Research Projects Agency, ironically with support from Charles Townes.
Unfortunately for Gould, the government declared the project classified, which meant that a security clearance was required to work on it. Because of his former participation in communist activities, Gould was unable to obtain a clearance. He continued to work at TRG, but was unable to contribute directly to the project to realize his ideas. Due to technical difficulties and perhaps Gould's inability to participate, TRG was beaten in the race to build the first working laser by Theodore Maiman at Hughes Research Laboratories.
According to wikipedia