The tr-ESFG of pristine monolayer MoS 2 is therefore composed of two components, one spectral component corresponding to the combined ground state bleach and stimulated emission signal, described by a single exponential, and the other spectral component corresponding to excited state absorption, described by double exponentials. We therefore apply a Global Analysis to the raw data in Figure based on the two-component model described by Eq. 2&3. The measured earlier negative signal is the combined signal of ground state bleach and stimulated emission, described by the red spectrum in Figure . It has a lifetime of 16.4 ps (𝑘 1 = 0.061 𝑝𝑠 -1 ), corresponding the exciton to trion relaxation timescale. The latter positive feature is described by excited state absorption, which has a biexponential dynamic, where the early rise is described by k 1 and the signal decays with a long lifetime of 129.0 ps (𝑘 2 = 0.0078 𝑝𝑠 -1 ). Interestingly, this excited state absorption signal peaks at 1.76 eV, indicating a 0.02 ~0.03 eV energy reduction due to the interaction between trions. This binding energy is smaller than bi-excitons .