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Previous and ongoing searches for extraterrestrial optical and infrarednanosecond laser pulses and narrow line-width continuous emissions have so farreturned null results. At the commonly used observation cadence of $\sim10^{-9}\,$s, sky-integrated starlight is a relevant noise source for largefield-of-view surveys. This can be reduced with narrow bandwidth filters,multipixel detectors, or a shorter observation cadence. We examine the limitsof short pulses set by the uncertainty principle, interstellar scattering,atmospheric scintillation, refraction, dispersion and receiver technology. Wefind that optimal laser pulses are time-bandwidth limited Gaussians with aduration of $\Delta t \approx\,10^{-12}\,$s at a wavelength$\lambda_{0}\approx1\,\mu$m, and a spectral width of $\Delta \lambda \approx1.5\,$nm. Shorter pulses are too strongly affected through Earth's atmosphere.Given certain technological advances, survey speed can be increased by threeorders of magnitude when moving from ns to ps pulses. Faster (and/or parallel)signal processing would allow for an all-sky-at-once survey of lasers targetedat Earth.

Interstellar communication. XI. Short pulse duration limits of optical SETI