(a) Reconstruction of the local electric near field (green line) and vector potential (red line) at the nanotaper surface from the measured streaking curve (symbols). The error bars indicate 95% confidence intervals of the Fermi fit. Retrieved wavelength-resolved (b) relative phase shift and (c) amplitude obtained from different measurements. Data points are shown as crosses, whose positions are given by the spectral sampling of the different measurements. Different measurement sets do not necessarily cover the same number and size of delay scans in the streaking spectrographs, which translates into a different spacing and number of data points after Fourier transformation. Only data points in the wavelength range covered by the input NIR pulses, that is, from 500 to 1,100 nm, are displayed. Data points outside this range are a consequence of over-sampling in the time domain, and have a vanishingly low spectral amplitude. Mean values (symbols) have been obtained by linearly interpolating the retrieved linear response from the individual measurements. Error bars represent the s.d. The green shaded areas show the range of phase shifts and relative amplitudes expected from the electric field calculations, considering emission from different points on the surface from the tapered nanowire.