<title>Targeted and all-sky search for nanosecond optical pulses at Harvard-Smithsonian</title>

Abstract

We have built a system to detect nanosecond pulsed optical signals from a target list of some 10,000 Sun-like stars, and have made some 20,000 observations during its two years of operation. A beamsplitter feeds a pair of hybrid avalanche photodetectors at the focal plane of the 1.5 m Cassegrain at the Harvard/Smithsonian Oak Ridge Observatory (Agassiz Station), with a coincidence triggering measurement of pulse width and intensity at subnanosecond resolution. A flexible web-enabled database, combined with mercifully low background coincidence rates (∼1 event per night), makes it easy to sort through far-flung data in search of repeated events from any candidate star. An identical system will soon begin observations, synchronized with ours, at the 0.9 m Cassegrain at Princeton University. These will permit unambiguous identification of even a solitary pulse. We are planning an all-sky search for optical pulses, using a dedicated 1.8 m f/2.4 spherical glass light bucket and an array of pixelated photomultipliers deployed in a pair of matched focal planes. The sky pixels, 1.5 arcmin square, tessellate a 1.• 6 × 0 .• 2 patch of sky in transit mode, covering the Northern sky in ∼150 clear nights. Fast custom IC electronics will monitor corresponding pixels for coincident optical pulses of nanosecond timescale, triggering storage of a digitized waveform of the light flash.

<title>Optical SETI observatories in the new millennium: a review</title>

“…This is done by the use of two identical optical detectors and coincidence detecting their outputs. This technique has been employed by Werthimer 43 , Horowitz 44 and others to essentially "eliminate" the background noise count problem. Based on ideas originally employed in the nuclear particle counting industry and later extended to OSETI by Werthimer and Horowitz.…”

“…This system is described elsewhere in these proceedings. 44 A system based on this technique is being installed at the Lick Observatory.…”

“…44 The new All-Sky Optical SETI Survey will use a 1.8 meter (72 inch) diameter optical telescope dedicated exclusively to SETI. When this "light-bucket" telescope is completed, it will be the largest in the eastern United States.…”

<title>Is there RFI in pulsed optical SETI?</title>

“…However, with forty years of steady Moore's Law growth in the laser industry, we can now contemplate sending continuous megawatt optical signals and petawatt (10 15 W) peak power optical pulses (demonstrated at picosecond and planned for nanosecond duration). 4 We have recently calculated that one of these modern pulsed lasers, directed with an equally modern 10 m telescope, would outshine our Sun by a factor of 5000 during its brief pulse in the direction of its slender beam 5,6 ; in other words, optical SETI transmission from Earth is possible. These developments have spurred several scientists to propose and develop experiments capable of detecting continuous wave (cw) and pulsed signals from other civilizations.…”

“…Wilson. 8 More recently, groups and individuals at Harvard, 5,6 Berkeley, 9 Santa Cruz (CA), 10 Princeton,…”