A reoccurring thought while I read this paper was “What the hell are masers?” I just kind of assumed they would be defined *somewhere.* Well, they’re not. So here’s what masers are: “microwave amplification by stimulated emission of radiation.” So lasers, but specifically in the microwave. The acronym was coined in 1953 when the first maser (I think) was successfully operational. Later, an “optical maser” was successfully created in 1960. The optical maser was first envisioned in 1957, and the term LASER (*light* amplification by stimulated emission of radiation) was coined that same year. Apparently Charles H Townes made the first ammonia maser:
Given this information, it makes sense that Townes would look into additional uses for his optical maser (from now on, just laser). At the time, SETI was new and exciting (well new-ish; the idea of contacting ET species had existed for centuries), and was not weighed down by the “giggle factor” that it experiences today. An inventor could write a paper like this, and receive mostly positive support for the idea without anyone calling BS or science-fiction on the idea. This paper, I believe, marks the first discussion of contacting ET species with lasers and possibly detecting such signals. These ideas have now been integrated, and other papers written on them, but the first to propose it is always the coolest (right?). Townes computes that with modern (from 1961) technology, we could already detect specific laser signals, and postulates that with only a bit more time (and narrow-band optical receivers) other laser signals would have high enough signal-to-noise to be detected.
One last note is I enjoy how Schwartz and Townes end their paper. The paper is fairly technical and a nice proof of concept, but they end the paper with a quick SETI discussion, saying that searches should go beyond the waterhole, that UCE and IR are absorbed by most atmospheres (so not to really bother with those), but also that a civilization more advanced than our own could have technology that we currently rule out as unfeasible. I do appreciate this throw-in, since we only ever look for traces that could have potentially been left by humans, since we need to set restrictions to actually make a search, but it is nice to acknowledge that other civilizations could be unlike us, and therefore could be communicating in ways unimaginable to us.