  Recently, helicity-dependent photocurrent was reported in Bi single thin fi
lms. It is proposed that the origin of this photocurrent is the combination of
photo-spin conversion and spin-charge conversion effects in Bi and efficient
spin conversion in Bi is expected. In this study, we measured two types of
terahertz (THz) emissions from Bi/Co bilayer films induced by spin current
generation using laser-induced demagnetization of the Co layer and photo-spin
conversion effect in the Bi layer to investigate the spin current induced by
the two mechanisms simultaneously. We clearly observed diff erent Bi thickness
dependence of peak intensity and that of bandwidth for THz spin current in two
experiments, i.e., spin current induced by demagnetization of Co and that by
photo-spin conversion in Bi. The different Bi thickness dependence of spin
current intensity and bandwidth in two experiments is caused by different spin
relaxation properties of optically excited spin currents in Bi layers.
