Example 2D IR spectra of the azide stretching mode at three waiting times collected in the fast-scan BoxCARS and pump-probe geometries are shown in Figure . In brief, the spectrum shows a pair of peaks corresponding to the ground-state bleach (red feature, on the diagonal) and the excited-state absorption (blue feature, below the diagonal). In general, the BoxCARS spectra (Figure ) preserve the defined shape of the main peaks throughout the 3 ps measurement window (Figure ). The minimal background in the spectra and the well-defined main peaks, even at long waiting times, highlight the quality of the spectra. It is worth noting that both the positive and negative peaks in the phased BoxCARS spectra show slight vertical elongation along the detection axis as compared to the pump-probe spectra. This can also be noted in the probe-axis projections and the diagonal slices. This peak elongation can be attributed to fifth-order signals which are more common in the BoxCARS geometry as a result of the high pulse energies .