  We report on the characterization by a position resolved laser system of
small-pitch 3D diodes irradiated with neutrons up to an extremely high fluence
of 3.5x10**16 neq cm**-2. We show that very high values of signal efficiency
are obtained, in good agreement with the geometrical expectation based on the
small values of the inter-electrode spacings, and also boosted by charge
multiplication effects at high voltage. These results confirm the very high
radiation tolerance of small-pitch 3D sensors well beyond the maximum fluences
expected at the High Luminosity LHC.
