Fig. 4: Comparison between time scans without and with silicon sample.

a Time-scan of the pump-probe delay without sample. The trace shows non-monotonic dynamics at early times attributed to the ultrafast response of the phase mask irradiated by the pump beam before diffracting the probe beam. At longer time delays the probe intensity increases, and no oscillation is detected. b Time-scan comparison of the diffraction (red) and transmission (blue) signals of crystalline silicon, showing a coherent oscillation of 16 ± 0.7 THz matching the Si optical phonon with frequency around 15.5 THz. The red/blue shaded area represents the signal including the standard deviation. The fits (lines) of the experimental traces are a guide to the eye and were performed using the TG equation and a linear term to follow the rise of the probe intensity (see text). The procedure and analysis used to extract the data points is described in the “Methods” Section.