Temporal wavefront and coherence maps.
(a) Wavefront curvature of a selected field cycle. The curved surface was interpolated from the centers of gravity of the measured local second order temporal autocorrelation functions within the line of highest field strength (from the 3D autocorrelation data set used in Fig. 3). It represents the spatial pulse front of a particular subcycle. (b), (c) Temporal coherence maps of few-cycle Gaussian (bottom, left) and Laguerre-Gaussian beams (bottom, right) were determined by autocorrelation measurements. The columns show distribution of the FWHM of the second order autocorrelation functions for temporal cuts along the propagation axes of all sub-beams (needle beams). The uncertainty of the FWHM of the local autocorrelation functions is less than ±400 attoseconds. Opposite angles of view were chosen for the two plots to better visualise the relevant features.