Energy spread compensation. a, Measured electron energy spectra for input beam (Blue shaded curve), accelerated beam without buncher (gray shaded curve) and with buncher (2×7 μJ THz: green shaded curve and 2×15 μJ THz: red shaded curve). The energy distribution is normalized to the 55 keV input electron beam with around 1 fC bunch charge. b, Measured input electron pulse duration with (red shaded curve) and without buncher (gray shaded curve). [9].