In the late 1940s, Townes started experimenting with microwaves and in 1951 he constructed a device that could generate and amplify these microwaves. Based on Einstein’s theory, Townes named his discovery “Maser” - an acronym for “microwave amplification by stimulated emission of radiation”. What was possible with microwaves, i.e. the amplification by stimulated emission of radiation, should also be possible for infrared or conventional light, knowing that as the wavelength decreases, the cost of constructing a laser greatly increases.
However, it was still a few more years before a “light amplification by stimulated emission of radiation”, or laser in short, was actually constructed based on this assumption. All the material required to build a laser was already known and available. A flash lamp, along with a synthetically manufactured ruby doped with chromium and a metal sleeve finally formed the first laser in the hands of the physicist Theodore Maiman in 1960. However, experts did not pay much attention to this discovery straight away. Quite the opposite: When Maiman attempted to have his findings printed in a journal, the editors refused to accept the text - the idea of combining coherent light beams with high color purity seemed too irrelevant and too meaningless.
It was only over the course of many years that it finally became clear what was truly possible with laser technology. Nowadays, a very broad range of laser systems exist. And all of these lasers are based on the same principle that Einstein predicted possible in 1917 and that Theodore Maiman experimentally demonstrated in 1960.