Fig. 3
Optical-pump optical-reflectivity-probe spectroscopy. a A schematic of the experimental setup. b Time evolutions of the reflectivity changes at 0.58 eV (red solid line), 0.694 eV (green solid line) and 0.96 eV (blue solid line). c Reflectivity change (\(\Delta R\)) spectra at 0.3 ps (black open circles), 1.0 ps (orange open circles), and 5.0 ps (blue open circles). The black solid line shows a reflectivity spectrum (\(R\)) polarized along the a-axis. The error bars are smaller than the data points. d Imaginary part of the dielectric constant (\(\varepsilon _2\)) spectrum (black solid line) and the change of \(\varepsilon _2\) (\(\Delta \varepsilon _2\)) spectrum (blue solid line) from the experimental results. e A schematic of the excitations of exciton, biexciton and two excitons. f ε2 spectrum (black solid line) and Δε2 spectrum (blue solid line) obtained by the theoretical calculations
