The laser was not discovered from a single breakthrough by one individual, but from a series of developments incorporating hundreds of great minds’ efforts, starting from Albert Einstein’s paper of “On the quantum theory of radiation” in 1917. Then Richard Tolman, Rudolf Ladenburg, and V.A Fabrikant brought up the ideas of negative absorption, stimulated emission, and population inversion, respectively. However, population inversion was never achieved experimentally until 1954 when Charles H. Townes and James P. Gordon made the first MASER (Microwave Amplification by Stimulated Emission of Radiation). Immediately after that, scientists started wondering how to make a MASER working at optical frequencies.
Starting from 1957, the competition of inventing an optical MASER began heating up. Teams at half a dozen laboratories set out, each hoping to be the first to succeed. The term “laser” was first introduced to the public in Gordon Gould’s 1959 conference paper. In 1960, Theodore Maiman was the first one to a demonstrate laser in ruby, which by the way was considered as a dark horse in this laser race. Over the next 30 years, Gordon Gould fought with the United States Patent and Trademark Office to obtain patents for the laser and related technologies, and was finally issued forty-eight patents, with optical pumping, collisional pumping, and applications patents being the most important.
The competition of developing new types of lasers did not end there. A brief review of important laser breakthroughs over the last 50 years will be presented.