  A femtosecond laser-irradiated crystallizing technique is tried to convert
amorphous Sb2Te3 film into crystalline film. Sensitive coherent phonon
spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb2Te3
film at the original irradiation site. The CPS reveals that the vibration
strength of two phonon modes that correspond to the characteristic phonon modes
of crystalline Sb2Te3, enhances with increasing laser irradiation fluence
(LIF), showing the rise of the degree of crystallization with LIF and that
femtosecond laser irradiation is a good post-treatment technique. Time-resolved
circularly polarized pump-probe spectroscopy is used to investigate electron
spin relaxation dynamics of the laser-induced crystallized Sb2Te3 film. Spin
relaxation process indeed is observed, confirming the theoretical predictions
on the validity of spin-dependent optical transition selection rule and the
feasibility of transient spin-grating-based optical detection scheme of
spin-plasmon collective modes in Sb2Te3-like topological insulators.
