Photoinduced Structural Dynamics of 2H-MoTe₂ Under Extremely High-Density Excitation Conditions

Through interband photoexcitation, a representative transitionmetal dichalcogenide (TMD) material, MoTe2, can undergovarious phenomena such as photothermal conversion, phase transition,nonlinear optical effects, and laser ablation depending on the excitationlevel. However, a comprehensive study of the photoinduced structuraldynamics of MoTe2 has yet to be performed because someof these phenomena interfere in a complex manner. In the present study,the photoinduced structural dynamics of 2H-MoTe2 was investigatedunder various excitation levels at a wavelength of 400 nm using ultrafasttime-resolved electron diffraction and transient reflection measurements.Photoexcitation induced coherent phonons for 1-2 ps, whichsubsequently decayed into isotropic thermal vibrations at & SIM;10ps. The amplitudes of the generated coherent phonon and thermal vibrationswere found to linearly increase as the incident fluence approached3-4 mJ/cm(2); however, the amplitudes remained nearlyconstant when the incident fluence ranged from 4-14 mJ/cm(2) due to saturable absorption. Multiphoton absorption processesmight be dominant above a fluence of 15 mJ/cm(2). Photoexcitationat high fluence (20-30 mJ/cm(2)) permanently damagedthe sample through laser ablation and tellurium segregation. The insightsin this study are critical for the further applicability and fundamentaloptical properties of photodevices based on TMD materials.