Fig. 3

Pump power and layer number-dependent transient SHG spectra. a TSHG spectra of the 13-nm ReS₂ crystal obtained at different pump fluences (0.6, 1.3, 3, and 8 mJ/cm²). The zoomed-in view of the dip near a zero probe delay (time zero) is illustrated in the inset. The respective SHG images are displayed on the top right. The scale bars correspond to 2 μm. The observed inverse carrier lifetime “1/τ” (bottom right) increases linearly with increasing pump fluence. b Normalized TSHG of the 2L to 16L ReS₂ crystals obtained with the 1.57-eV pump and 1.19-eV probe beams. c Representative SHG images captured at different probe delay times. The carrier lifetime (τ) as a function of the number of layers is plotted at the bottom. The uncertainties of the extracted lifetime are also projected, including error bars. All the scale bars correspond to 5 μm