The pulse shaper was triggered by the Ti:Sapphire laser system at 1000 Hz repetition rate. A series of mask files were uploaded to the memory of an arbitrary waveform generator (AWG, PXDAC4800, Signatec) before the experiment started. Those masks were programmed by LabVIEW (National Instruments) and controlled the waveform of the acoustic wave, which shaped the input laser pulse into four pulses in time. When receiving a start data collection signal, one of the masks was set active and sent into an RF amplifier, which modulated the digital signal into an acoustic wave that propagated through the germanium AOM crystal. The crystal served as a programmable diffraction grating, allowing for pulse shaping in the frequency domain. For each mass spectrometer cycle (10 Hz), 100 identical pulse trains were directed into the trap to accumulate photoproduct intensity. 16 mass spectrometer cycles were averaged for photodissociation yield of one pulse train (i.e., the same mask was used to shape the ultrafast laser pulse 1600 times, averaged over 16 mass spectrometer cycles). The data collection program would send a switching signal to the AWG after finishing data collection of the previous mask. AWG would stop current mask and would start the next mask immediately.