  The nature of electronic motion and structural information of atoms and
molecules is encoded into strong-field induced radiations ranging from
terahertz (THz) to extreme ultraviolet wavelength. The dependence of THz yields
in bi-chromatic laser fields on ellipticity and interpulse phase delay were
experimentally measured, and the trajectory calculations establish the link
between the THz emission and the motion of the photoelectron wave packet. The
interaction between the photoelectron and parent core transforms from soft
collision to recollision as the laser field tuned from elliptical to linear
polarization, which can be reflected in THz emission. The soft collision is
found to be more effective in reconstructing electron dynamics through THz
polarization, which enables to construct the effective core potential of the
generating medium with the Coulomb-reshaped THz radiation in an elliptically
polarized laser field. Our work allows designing innovative all-optical THz
measurements of electronic and structural dynamics.
