  Near-infrared (NIR) pump-terahertz (THz) probe spectroscopy is used to
investigate the charge and spin exciations in a strongly correlated electron
compound Na0.5CoO2. This compound exhibits a coexistence of various charge and
spin orders arising from intricate interactions among charge, spin, and orbital
degrees of freedom. NIR pulses create significantly diverse effects on the
charge and spin orders; while the charge order is easily melted,coherent magnon
excitations are present in all fluences examined. Furthermore, a novel {\pi}
phase shift of the coherent magnon oscillations is observed in the pump-induced
change of the terahertz electric field between regions of increasing and
decreasing field change. These results unequivocally illustrate that ultrashort
laser pulses enable the disentanglement of different interactions within
complex systems characterized by multiple orders, providing a fresh perspective
on the interplay between itinerant and localized electrons within the Co 3d t2g
multiplets.
