  We report the ultra-fast optical response of quasi-particles (QPs) in both
the pseudogap (PG) and superconducting (SC) states of underdoped (UD)
Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ (Bi2212) single crystal measured with
the time-resolved pump-probe technique. At a probe energy
$\hbar\omega_{pr}$=1.55 eV, it is found that the reflectivity change
$\Delta$R/R changes its sign at exactly $T_{c}$, which allows the direct
separation of the charge dynamics of PG and SC QPs. Further systematic
investigations indicate that the transient signals associated with PG and SC
QPs depend on the probe beam energy and polarization. By tuning them below
$T_{c}$ two distinct components can be detected simultaneously, providing
evidence for the coexistence of PG and SC QPs.
