A major challenge in collecting nonlinear action spectra is that each pulse is capable of exciting the system individually, leading to a constant background signal. Further, interaction from a pair of pulses can contribute a linear background signal. To isolate the desired nonlinear transient absorption signal that arises from population modulation due to interactions with all three pulses, an 8-step phase cycling scheme was employed. For each pathway, there are two simultaneous interactions with the pump pulse. These interactions place the system into either the |0⟩⟨0| or |1⟩⟨1| population state. In the ground-state bleach (GSB) pathway, the first probe pulse interaction switches the system from |0⟩⟨0| into the |1⟩⟨0| coherence state. This coherence evolves during the probe pair delay time τ as e -iω 10 τ . The second probe pulse interaction places the system into the |1⟩⟨1| population state and modulates the excited-state population as a function of τ. The stimulated emission (SE) pathway likewise proceeds through the |1⟩⟨0| coherence state and ends in the |1⟩⟨1| population state. These pathways are analogous to the GSB and SE pathways (which we will collectively refer to as bleaches) in condensed-phase experiments. Both bleach pathways give rise to an overall time-dependent signal that oscillates as -e -iω 10 τ with an intensity proportional to |⟨1|𝜇|0⟩| . Therefore, a decrease in signal will be observed at the fundamental transition frequency ω10.