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Detectability of Pulsed Laser Beacons



Diagram illustrating photon-counts as a function of range. (20068 bytes)


This (3-dimensional) diagram illustrates the photon-count for both large and small receiving telescopes for an attention-getting ETI laser pulse of 1 ns duration at a repetition rate of 1 Hz. It is assumed that the ETI civilization is capable of producing a peak EIRP = 3.2 x 1033 W. The photon-count rates are shown for ranges of 10, 100 and 1,000 light years, with the very modest assumption that the overall detection efficiency is only 1%. A star like out Sun appears as a 2nd magnitude object at a range of 10 light years. During each 1ns pulse, the laser outshines the ETI's star by approximately ten million times. Not only is the detectability of the pulse not affected by the stellar background noise, but light pollution has little effect if a spatial filter is employed to confine the field-of-view to that surrounding the star under observation.  Calculations in support of this diagram may be found in 9501-001.


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