These Liouville pathways (Feynman diagrams) can be categorized as either rephasing or non-rephasing signals, based on the phase accumulated by the signal after the application of the third laser pulse. These signals can be further partitioned into three physical processes, namely, stimulated emission (SE), ground-state bleaching (GSB), and excited-state absorption (ESA). For notation purposes, we only write the first four Liouville pathways in Eq. 4a -Eq. 4d