Fig. 6
Relativistic ultrafast point-projection microscopy calibration. a Scanning electron microscopy (SEM) of the resolution target used to determine the contrast transfer function (CTF) of the instrument. The Ronchi rulings are labeled with the mean bar width (w) and spacing (s) as measured by SEM. b Ultrafast electron point-projection image of the target. Line profiles were extracted from the red and blue regions for resolution analysis. c Contrast transfer function of the instrument for both x and y lateral dimensions. Contrast values obtained from the measured line profiles at f0, the fundamental frequency, and \(\frac{{f_0}}{2}\) are plotted as points (filled for f0, empty for \(\frac{{f_0}}{2}\)) and fit with Gaussian CTFs (solid curves). Error bars represent one standard error above and below the measured contrast value. \(\sigma _{{\mathrm{x}},{\mathrm{psf}}}\) and \(\sigma _{{\mathrm{y}},{\mathrm{psf}}}\) are the standard deviations of Gaussian point spread functions (PSFs) corresponding to the best-fit CTFs. These are shown with the standard error estimated from fitting error. The inset shows the measured ruling profiles (points) superimposed with model profiles (curves) computed by applying the best-fit CTF to step functions with the SEM-measured dimensions. For a detailed description of CTF determination, see the Methods section
