Exploring optical SETI's middle ground

Abstract

The Search for Extra-Terrestrial Intelligence (SETI) in optical wavelengths has recently concentrated either on detecting intense short light pulses that briefly outshine the background star or on finding unique features that stand out in the star's spectrum. But there is a middle ground available where the temporal variation of an optical SETI source would distinguish it from its stellar background. Initial results are presented for frequency-domain searches, covering a signal range of 1–10,000 Hz, with an instrument that simultaneously measures two broad optical spectral bands. It is shown that signals a thousand times fainter than the background starlight can be detected using this instrument coupled to a meter-class telescope. Since these signals can be either positive or negative (i.e. a periodic obscuration), the intriguing possibility exists of detecting signals where no energy need be intentionally beamed toward Earth.