Optical SETI is the search for visible or infrared signals from extraterrestrial civilizations.
Many of the recent developments in optical SETI have stemmed from the SETI Institute sponsored "SETI Science and Technology Working Group", a team of international scientists preparing a plan for new directions for SETI searches and systems over the years 2000-2020. Members of the optical SETI sub-group include Eric Becklin, John Carlstrom, Sandy Faber, Giovanni Fazio, Paul Horowitz, Mike Lampton, Larry Lesyna, Geoff Marcy, Seth Shostak, Charles Townes, and Dan Werthimer (chair).
One of the two seaches at Berkeley is a search for laser signals that are on continuously, or at least a large fraction of the time. This search, directed by Geoff Marcy, is a 1000 star program to search for ultra narrow band signals in the visible. They plan to search though thousands of extremely high resolution spectra for very sharp lines (lines which are not thermally broadened). Much of the data has already been taken by Marcy and Butler in their ongoing planet search, and more data is coming in all the time, mostly from Lick and Keck observatories, and some from the Southern Hemisphere search for planets in Australia.
The Berkeley pulse search plans to observe 2500 nearby stars, looking for very short bright pulses that might last a billionth of a second or so, perhaps transmitted by a powerful pulsed laser operated by a distant civilization. The target list includes mostly nearby F,G,K and M stars, plus a few globular cluster and Galaxies.
The pulse search, directed by Dan Werthimer, utilizes UC Berkeley's 30 inch automated telescope at Leuschner observatory and an instrument originally built for optical SETI in 1997 (for a picture of the telescope, click here). A block diagram of the current instrument is shown in figure 1 (the original used only two PMTs).
The system uses of a beam splitter to feed light from the telescope into three ultra high speed photomultiplier tubes, each followed by a high speed amplifier, a fast disriminator, and coincidence detectors. Three detectors are needed to reject "false alarms", which can be caused by radioactive decay and scintillation in the PMT glass, cosmic rays,
and ion feedback. These "false alarms" can happen often in a single PMT, rarely in two, but almost never in three PMT's simultaneously.
Our next generation optical SETI instrument—Open Source Pulsed Optical SETI Hardware (OSPOSH) is based on the same front-end optics and photodetectors as the original Berkeley OSETI instrument, but adds a flexible digital back-end based on the Center for Astronomy Signal Processing and Electronics Research (CASPER) DSP instrument design system. The programmable FPGA-based digital back-end will allow us to improve sensitivity by implementing sophisticated real-time detection algorithms, capture large swaths of raw sampled voltages for diagnostics or centroiding and perform efficient rejection of interference based on pulse profiles.
For details on our next generation effort, visit the CASPER Wiki.
For details on the original instrumentation and software, visit the Leuschner/Lick Technical Details page or see Leuschner Observatory's Optical SETI page.