The search for pulsed and continuous wave laser beacon signals from intelligent extraterrestrials in the visible and infrared part of the spectrum. The idea was first suggested in 1961 only a year after the Nobel-winning invention of the maser by Townes and Schalow but received little attention at the time because radio technology was in a much more mature state. Indeed, over the past few decades there have been many, large-scale SETI programs aimed at detecting artificial microwave signals but only a handful designed to operate in the visible/infrared region. That situation is now changing as a result both of the rapid development of laser technology and the realization by astronomers that optical communications over interstellar distances makes good, practical sense.
As an alternative to radio waves for sending messages to the stars, lasers offer a number of advantages. They are not produced as "noise" by natural processes and are highly distinctive. Quasars, pulsars, and black holes were all found or confirmed because of their unique radiation characteristics, not because of their resemblance to ordinary stars. So, it may be that a civilization wanting to send a message would choose an "unnatural" wavelength or technology to achieve maximum contrast to the natural environment (an argument directly counter to that used in support of 21-centimeter line SETI). Lasers also have the advantage that they can be aimed accurately at a target, thereby enabling the best use of the transmitted energy. A well-designed laser would be very bright with a high signal-to-noise ratio. Optical communication, enabling five times as much information to be carried, would be the logical choice for an advanced civilization, argued Russian astronomer Viktory Shvartsman. A search for such signals, begun in 1989, was carried out using the BTA-6 optical telescope (then the world's largest) of the Soviet Union's Special Astrophysical Observatory in the Caucasus, linked to a computer and another instrument, known as MANIA. The wide bandwidth available at optical frequencies could be exploited for sending complex, information-rich signals. This could even include, suggested John Rather of the Kaman Aerospace Corporation, the genetic code for a human being (see genetic code, interstellar transmission).
Many of the most recent developments in optical SETI stemmed from the discussions of the 1998 "SETI Science and Technology Working Group," sponsored by the SETI Institute. In the wake of this, the Planetary Society and the SETI Institute funded projects at the University of California, Berkeley (see optical SETI at Berkeley) and Harvard University (see optical SETI at Harvard/Smithsonian) to search for laser signals coming from nearby Sun-like stars, as well as from globular clusters and external galaxies. A separate search is underway at the Columbus Optical SETI Observatory.
Related category SETI
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