  The momentum and temperature dependence of the superconducting gap and
pseudogap in optimally-doped Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_6$ superconductor
is investigated by super-high resolution laser-based angle-resolved
photoemission spectroscopy. The measured energy gap in the superconducting
state exhibits a standard {\it d}-wave form. Pseudogap opens above T$_c$ over a
large portion of the Fermi surface with a "Fermi arc" formed near the nodal
region. In the region outside of the "Fermi arc", the pseudogap has the similar
magnitude and momentum dependence as the gap in the superconducting state which
changes little with temperature and shows no abrupt change across T$_c$. These
observations indicate that the pseudogap and superconducting gap are closely
related and favor the picture that the pseudogap is a precursor to the
superconducting gap.
