Despite the similarity to TA, a striking difference between tr-ESFG and TA are the signs of their signals. In the context of double-sided Feynman diagram, every interaction with ket states introduces a positive sign in the signal, whereas its counterpart with the bra states leads to a negative sign. Note the final emission (curly arrow) does not contribute to the sign here and an extra negative sign needs to be included between the ESFG (2 nd order signal) and tr-ESFG (4 th order) due to the extra 𝜋 2 phase flip after every interaction. Following this convention, the ground state bleach signal is negative (i.e. a 𝜋 phase difference relative to static ESFG), while both stimulated emission and excited state absorption signals are positive (i.e. in phase relative to static ESFG). Intuitively, this can be understood that for ground state bleach, the transition from ground state to trion is reduced because the population of the ground states decrease upon optical pumping. For stimulated emission and excited state absorption, both signals increase from the trion population. The former stimulates ESFG signal while the latter can only emit signal upon the creation of trions. The signal is in a sharp contrast to TA, in which ground state bleach and stimulated emission have the same sign and they often overwhelm the spectra. Here, because ground state bleach and stimulated emission have opposite phases and they both emit from trions, they cancel each other.