Extended Data Fig. 9: Amplitude scaling of the weak-field terahertz pulse.
a,b, Normalized weak-field waveforms, VWF(t), acquired at VSF,pk = –10 V (a) and VSF,pk = +10 V (b) for weak-field peak terahertz voltages of VWF,pk = ±0.30 V (black line), VWF,pk = ±0.24 V (red line), VWF,pk = ±0.18 V (blue line), VWF,pk = ±0.12 V (green line), and VWF,pk = ±0.09 V (purple line). The measurements were performed on Au(111) at constant current with Vd.c. = 10 mV, Id.c. = 200 pA. c,d, ΔQTHz–VWF,pk curves acquired at τCC = 0 fs (orange line) and τCC = –530 fs (purple line) for a negative-dominant terahertz polarity at VSF,pk = –10 V (c) and a positive-dominant terahertz polarity at VSF,pk = +10 V (d). The insets within c and d show the corresponding verified weak-field terahertz waveforms measured with THz-CC. The weak-field waveform has an inverted polarity with respect to the strong-field waveform due to the experimental geometry (see Fig. 1). The orange and purple circles within the insets indicate the temporal locations of the corresponding measurements. The measurements were performed on Au(111) at constant height with Vd.c. = 0 V and the tip–sample separation set by V0 = 10 mV, I0 = 300 pA. The dashed black lines are linear fits to the data.
