An Au uniform photocathode underlayer is employed in this paper to obtain picosecond (ps) optical gating width for image intensifier tube. The transmittances and gating pulse transmission efficiencies of the underlayer with different thicknesses are tested and compared to determine the optimal thickness. An 18 mm diameter proximity focused microchannel plate image intensifier tube with S25 photocathode is fabricated using this uniform underlayer. The profile measurement shows the tube has an optical gating time as low as 230 ps full width at half maximum (FWHM) when gated with a 176 ps width gating pulse. The measured iris delay is between 83 ps and 108 ps, which approaches the theoretical limit of its kind.