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Quantum dot samples used in this study were synthesized using the hot injection method.\cite{Wehrenberg2002}
Samples were kept in a glovebox after synthesis and exposure to visible and UV light was minimized.
These conditions preserved the dots for several months.
Two samples, Batch A and Batch B, are presented in this study, in an effort to show the robustness of the results.
Properties of their optical characterization are shown in Table \ref{tab:QD_abs}.
The 1S band of Batch A is broader than Batch B, an effect which is usually attributed to a wider size distribution and therefore greater inhomogeneous broadening.
\begin{table}[]
\centering
\caption{Batch Parameters extracted from absorption spectra. $\langle d \rangle$: average QD diameter, as inferred by the 1S transition energy. }
\label{tab:QD_abs}
\begin{tabular}{l|cc}
& A & B \\
\hline
$ \omega_{10} \left( \text{cm}^{-1} \right)$ & 7570 & 6620 \\
$ \text{FWHM} \left(\text{cm}^{-1}\right) $ & 780 & 540 \\
$ \langle d \rangle \left(\text{nm}\right)$ & 4 & 4.8 \\
$ \sigma_0 \left( \times 10^{16} \text{cm}^2 \right)$ & 1.7 & 2.9
\end{tabular}
\end{table}
The experimental system for the TG experiment has been previously explained.\cite{Kohler2014,Czech2015}
Briefly, two independently tunable OPAs are used to make pulses $E_1$ and $E_2$ with colors $\omega_1$ and $\omega_2$.
The third beam, $E_{2^\prime}$, is split off from $E_2$. The TG experiment utilized here uses temporally overlapped $E_2$ and $E_{2^\prime}$.
Previous ultrafast TG work has characterized the delay of $E_1$ as $\tau_{21}=\tau_2-\tau_1$; to connect the experimental space with the TA measurements, we will report the population delay time between the probe and the pump as $T(=-\tau_{21})$.
Pulse timing is controlled by a motorized stage that adjusts the arrival time of $E_1$ relative to $E_2$ and $E_{2^\prime}$.
All three beams are focused onto the sample in a BOXCARS geometry and the direction $\vec{k}_1-\vec{k}_2+\vec{k}_{2^\prime}$ is isolated and sent to a monochromator to isolate the $\omega_1$ frequency with $\sim 120 \text{cm}^{-1}$ detection bandwidth.
The signal, $N_{\text{TG}}$, was detected with an InSb photodiode. Reflective neutral density filters (Inconel) limit the pulse fluence to avoid multi-photon absorption.
To control for frequency-dependent changes in pulse arrival time due to the OPAs and the neutral density, a calibration table was established to assign a correct zero delay for each color combination (see supporting information for more details).
The TA experiments were designed to minimally change the TG experimental conditions.
The $E_{2^\prime}$ beam was blocked and signal in the $\vec{k}_1$ direction was measured.
$E_2$ was chopped and the differential signal and the average signal were measured to define $T_0$ and $T$ needed to compute $\Delta A$.
Just as in TG experiments, the excitation frequencies were scanned while the monochromator was locked at $\omega_m=\omega_1$.
% DK: perhaps leave this part out
%Finally, fluence studies resonant with the 1S band were performed to test for indications of intensity-dependent relaxation.
%These studies showed no indication of accelerated Auger recombination rates (see supporting info).
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