  A kagome lattice of 3d transition metals hosts flat bands, Dirac fermions and
saddle points. It provides a versatile platform for achieving topological
superconductivity, anomalous Hall effect, unconventional density wave order and
quantum spin liquid when the strong correlation, spin-orbit coupling or
magnetic order are involved in such a lattice. Here, using laser-based
angle-resolved photoemission spectroscopy in combination with density
functional theory calculations, we investigate the electronic structure of the
newly discovered kagome superconductor CsTi$_3$Bi$_5$, which is isostructural
to the AV$_3$Sb$_5$ (A=K, Rb or Cs) kagome superconductors and possesses a
perfect two-dimensional kagome network of Titanium. We directly observed a
strikingly flat band derived from the local destructive interferences of Bloch
wave functions within the kagome lattices. We also identify the type-II Dirac
nodal loops around the Brillouin zone center, the type-III Dirac nodal loops
around the zone corners and type-III Dirac nodal lines along the k$_z$
direction. In addition, around the Brillouin zone center, Z2 nontrivial
topological surface states are also observed which is formed from the band
inversion due to strong spin orbital coupling. The simultaneous existence of
such multi-sets of nontrivial band structures in one kagome superconductor not
only provides good opportunities to study related physics in the kagome lattice
but also makes CsTi$_3$Bi$_5$ an ideal system to realize noval quantum
phenomena by manipulating its chemical potential with chemical doping or
pressure.
