Fig. 4: Electron spectrometer calibrations with electrons modulated at four different optical frequencies.
From: Unifying frequency metrology across microwave, optical, and free-electron domains
a Deviations of the calibration markers at multiples of the photon energy from the nominal energy of the spectrometer. Shaded areas correspond to error bars. b First-order components of the polynomial fits of the energy solutions (pixel-to-energy mappings) for the four calibrations, showing the calibrated average dispersions. Errors in optical frequencies measured from electron spectra before (c) and after (d) calibrating the electron spectrometer with electrons modulated at the optical frequency of 194 567 516 MHz. Error bars in (c) are derived from the maximal deviation of the pre-calibration nominal dispersion from the calibrated dispersion, and error bars in (d) are obtained from the calibration uncertainty of the average dispersion.
