and ( ) the inverse homogeneous lifetime T Hom -1 . The calibration mismatch error δω 1 effectively acts like a zero-order frequency shift along the pump axis which accounts for a finite error in the independent calibrations of the pump and probe axes. Though calibration errors are not present in the simulated data, we still treat the fitting as we would with experimental data, where this parameter may be necessary. δω 1 is also useful for fitting to phase distorted data, as shown SI section G. The Kubo amplitude scaling factor β may partially account for situations where dephasing does not scale harmonically between the 0-1 and 1-2 transitions. We tend to find that fitting to inverse lifetimes and squared amplitudes, i.e. T Hom -1 and Δ 2 , is more stable than T Hom and Δ, which is not surprising given that T Hom -1 and Δ 2 appear linearly in exponential arguments of the response function model. At the end of every iteration the program checks to ensure that the next movement 𝐩𝐩 + 𝚫𝚫𝐩𝐩 is within user-defined boundaries. This routine could be modified to