Tracking the anisotropic electron dynamics in SnSe by time- and polarization-resolved high-harmonic spectroscopy

The anisotropic electronic properties of SnSe provide distinctive opportunities for studying polarization-dependent carrier dynamics. However, resolving such directional effects remains challenging for conventional spectroscopy techniques. Here, time-resolved high-harmonic spectroscopy (TR-HHS) is utilized to capture the anisotropic ultrafast processes in SnSe thin film. The TR-HHS signal evolves over the hundred-femtosecond to few-picosecond regime and demonstrates strong crystal orientation dependence. These results are attributed to anisotropic electronic relaxation encompassing electron thermalization and phonon-mediated hot-electron cooling. Our findings demonstrate that TR-HHS can serve as a powerful all-optical tool for probing symmetry-governed electron dynamics in anisotropic materials and provide new strategies for developing polarization-tunable optoelectronic devices.