Optical Detection of Lasers with Near-term Technology at Interstellar Distances

This paper examines the ability to produce a laser beam detectable to a cursory survey (SNR 0.1% with a 1 m receive telescope) by an extraterrestrial intelligence using proven or near-term technology (megawatt-class lasers, telescopes tens of meters in size). We find that such lasers can produce a signal at ranges of less than 20,000 lt-yr, with a broad enough beam to overcome uncertainties in nearby exoplanet orbits (e.g., Prox Cen b) or encompass entire habitable zones of more distant systems (e.g., TRAPPIST-1). While the probability of closing a handshake with even a nearby extraterrestrial intelligence is low with current survey methodologies, advances in full-sky surveys for SETI and other purposes may reduce the mean-time-to-handshake to decades or centuries, after which these laser systems may close links at data rates of kbps-Mpbs. The next major gap to address for searching for extraterrestrial lasers is in expanding spectral searches into the infrared, where most terrestrial communication and high-power lasers are manufactured.