Fig. 3: Enhancing X-ray intensity by velocity matching the laser intensity peak and electrons.
From: Metasurface-based multi-harmonic free-electron light source
The maximum intensity for positive and negative emission orders are presented in (a) and (b), respectively. The inset shows the output spectrum for θi =0, and the arrow colors are used to distinguish the different emission orders: order 0 (green), order 1 (blue), order 2 (red), and order 3 (black). Solid (dashed) lines represent the 7.5-MeV (100 keV) electron energy and the dots are approximated in Equations 3 and 4. The logarithmic spectrum in (c) shows the peak intensities and energies for the ± 1 emission orders at different angles of incidence of the laser pulse. The metasurface considered has a period of 30 nm consisting of silver blocks 15 nm in width and 40 nm in height laying on a substrate with a refractive index of 1.5, and the spectrum is measured in the direction of the electrons
