Fig. 2

Observation of tunable radiation from silicon in the 800–1600 nm window. Experimental (top) and simulated (bottom) spectral efficiencies recorded for various kinetic energies (a) (9–20 keV) from 278 nm-period gratings and (b) (2–6 keV) from 139 nm-period gratings. The incident electron current and measured output powers are reported in the colored boxes for each measurement. Dashed lines correspond to the predicted output wavelength at normal emission direction from the SP energy-angle equation. Optical and quantum efficiencies are reported in the SI, section I. Error bars (shaded area) are estimated from the standard deviation of the background signal