Search for Nanosecond Optical Pulses from Nearby Solar‐Type Stars

Abstract

With "Earth 2000" technology we could generate a directed laser pulse that outshines the broadband visible light of the Sun by four orders of magnitude. This is a conservative lower bound for the technical capability of a communicating civilization; optical interstellar communication is thus technically plausible. We have built a pair of systems to detect nanosecond pulsed optical signals from a target list that includes some 13,000 Sun-like stars, and have made some 16,000 observations totaling nearly 2400 hours during five years of operation. A beamsplitter-fed pair of hybrid avalanche photodetectors at the 1.5 m Wyeth Telescope at the Harvard/Smithsonian Oak Ridge Observatory (Agassiz Station) triggers on a coincident pulse pair, initiating measurement of pulse width and intensity at sub-nanosecond resolution. An identical system at the 0.9 m Cassegrain at Princeton's Fitz-Randolph Observatory performs synchronized observations with 0.1 µs event timing, permitting unambiguous identification of even a solitary pulse. Among the 11,600 artifact-free observations at Harvard, the distribution of 274 observed events shows no pattern of repetition, and is consistent with a model with uniform event rate, independent of target. With one possible exception (HIP 107395), no valid event has been seen simultaneously at the two observatories. We describe the search and candidate events, and set limits on the prevalence of civilizations transmitting intense optical pulses.

Spectral signatures of ultra-rapidly varying objects in spectroscopic surveys

“…The effect will depend on position and distance, being worse in the direction of the Galactic plane and minimum near the Galactic poles. In the worse-case scenario (in the Galactic disk) the reduction in pulse height is modest (less than 10%) at visible wavelengths for distances less than 500 pc but becomes unmanageable, within the Galactic disk, at substantially greater distances (Howard et al 2004). The effect would be negligible in the direction of the Galactic poles.…”

“…Scattering effects from the interstellar medium can be severe for very distant objects (Howard et al 2004), thus reducing the contrast of the spectral modulation, but are negligible for nearby objects. The effect will depend on position and distance, being worse in the direction of the Galactic plane and minimum near the Galactic poles.…”

“…This would allow us to directly observe pulses separated by times shorter than 10 −10 s with standard spectroscopic equipment in the visual-infrared regions of the spectrum. One could measure time separations orders of magnitude shorter than the nanosecond time separation limits of current techniques (e.g., Howard et al 2004).…”

Optical Seti Observations of the Anomalous Star Kic 8462852

“…An advanced technological civilization seeking to signal evidence of its existence at interstellar distances might do so using a powerful laser with pulse duration in the nanosecond range (Schwartz & Townes 1961;Howard & Horowitz 2001;Howard et al 2004). Stars with known exoplanets have been targeted in past SETI searches , with exoplanets discovered by the Kepler mission being of particular interest because any electromagnetic communications between planets would be along an orbital plane viewed edge-on from the perspective of our solar system, making it conceivable we could detect this spillover radiation (Tellis & Marcy 2015).…”

Pulsenet - A Parallel Flash Sampler and Digital Processor IC for Optical SETI

“…The scope of these searches is frequently limited by technology-in radio SETI, the FFTs performed by ever expanding arrays of FPGAs, DSPs, and PCs have greatly increased the spectral coverage and sensitivity. Optical SETI before PulseNet was limited to observing candidate stars one at a time (~104 stars and ~10-5 of the sky area observed in several years) [1]. With PulseNet, we can survey the entire Northern sky for optical signals in less than a year.…”