A scheme of the fast-scan BoxCARS setup is shown in Figure . The mid-IR source beam is routed through a 50/50 ZnSe beam splitter (BS) to generate the "pump" (transmitted) and "probe" (reflected) beams. The pump pulse is sent through the pulse shaper (QuickShape, PhaseTech Spectroscopy), which is based on an acousto-optic modulator (AOM), to generate a pair of time-delayed pump pulse pairs (k1 and k2). Electronically modulating the pump pulses allows for precise control of t1 to eliminate timing instabilities or drift from mechanical stages used in traditional BoxCARS setups. A 50/50 ZnSe BS at the pulse shaper output creates a copy of the modulated output pair (k1' and k2'). Adding a t1 delay between two pump pulses in each pair, the rephasing (SR) and nonrephasing (SNR) signals are simultaneously generated in same direction after the beam interactions of