The first proposal for Optical SETI

This 1961 paper by R.N. Schwartz and Charles Townes, discusses using Optical Masers (Lasers) for communication across interstellar distances. I feel that it is worth noting that this falls closely on the Cocconi and Morrison paper of 1959 which first suggested the water-hole in the radio as the ideal place to look for, for intelligent extra terrestrial (ETI) civilization.

The authors talk about the recent discovery of ruby optical Masers  by Townes. Since the M in Masers is for Microwave, optical Masers, were soon called Lasers or Light Amplification by Simulated Emission of Radiation.

The authors consider using Optical Masers (Lasers) on two different systems and compare the two. One is a laser on a 200 inch telescope (like the 200 inch Hale Telescope), whereas the other is 25 individual 4 inch  telescopes with Lasers pointed in the same direction. They consider atmospheric seeing as a limiting factor and hence consider that the 25 individual small telescopes might be a better option. I think this paper was really advanced for its time, since 4 years after the launch of Sputnik (1957) it considers the use of Adaptive optics and space telescopes.

It also considers the detectability of Lasers using 1961 technology levels for laser power and detectability. The paper also talks about high resolution spectrometers which could spectrally resolve the laser and hence detect that this artificial beacon outshines the host star. This would be a hallmark of its artificial origins.

The paper concludes by noting that the water hole in the radio should not be the only region where we look for interstellar communication. It also mentions that an advanced ETI might develop capabilities that we have ruled out and consider impractical.

Optical SETI is not exactly a novel approach, but one that has not yet been pursued in earnest. There have been recent efforts by Andrew Howard, Shelley Wright, Nathaniel Tellis in this direction. We must take advantage of the vast resources that are plowed by the astronomical community in this direction and utilize the instruments, development and data sets that exist as a product of this.