How could a pulsed laser signal stand out from the light of a distant star?

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artist's conception of Kepler-186f — extraterrestrial intelligence An artist's conception depicts Kepler-186f, the first Earth-sized extrasolar planet found in its star's habitable zone.

A pulsed laser signal can be distinguished from the light of a distant star by concentrating its energy into extremely brief, high-power bursts. While a star emits light continuously, a civilization using lasers can fire pulses lasting a nanosecond or less.12

By compressing the output energy into such a short duration, the signal can momentarily outshine the natural light emitted by the star. Because laser light is monochromatic and highly coherent, these brief flashes create a distinct signature that differs significantly from the steady, broad-spectrum light produced by stellar processes. Researchers use sensitive photomultiplier tubes attached to telescopes to detect these rapid, intense flashes as part of Optical SETI efforts.21