Optical SETI

The SETI Institute, along with scientists from the University of California's Lick Observatory, UC Santa Cruz, and UC Berkeley has coupled the Lick Observatory's 40-inch Nickel Telescope with a new pulse-detection system capable of finding laser beacons from civilizations many light-years distant. Unlike other optical SETI searches, this experiment is largely immune to false alarms, due to a novel approach incorporating 3 light detectors.

"This is perhaps the most sensitive optical SETI search yet undertaken," said Frank Drake, Director of the Carl Sagan Center for the Study of Life in the Universe. 

Drake, who in 1960 conducted the first modern hunt for evidence of extraterrestrial intelligence, is usually associated with radio SETI, an approach in which large antennas are connected to specialized, multi-million channel receivers.

"This is different," noted Drake. "We are looking for very brief but powerful pulses of laser light from other planetary systems, rather than the steady whine of a radio transmitter."

While optical SETI has been undertaken before, it is only recently that major experiments, scrutinizing hundreds or even thousands of star systems, have been initiated. This is largely the consequence of a study conducted by the SETI Institute during the years 1997 - 1999 which showed that new technology has made optical SETI an appealing approach for finding technologically sophisticated civilizations. 

However, unlike its radio counterpart, optical SETI requires that any extraterrestrial civilization be deliberately signaling in the direction of our solar system.

The experiment is unique in exploiting three light detectors (photomultipliers) to search for bright pulses that arrive in a short period of time (less than a billionth of a second). Of course, light from the central star will trigger the detectors as well, but seldom will all three photomultipliers be hit by photons within a billionth of a second time frame. The expected number of false alarms for the stars being looked at is about one per year. Other optical SETI experiments use only one or two detectors and have been plagued by false alarms occurring on a daily basis. 
Starlight, cosmic rays, muon showers, and radioactive decays in the glass of photomultiplier tubes can all contribute confusing "events" to optical SETI searches. 

"One great advantage of optical SETI is that there's no terrestrial interference," comments Drake. "It's an exciting new field."