Fig. 2: Transverse recoil effects in the spectra of CXR.
From: Transverse recoil imprinted on free-electron radiation
a, c, and e plot the angular spectral distribution of quantum CXR. b, d, and f compare the spectra of quantum CXR and classical CXR at the radiation angle \(\theta=100^\circ\). The curves in (a, c, e) and the radiation peaks of quantum CXR in (b, d, f) are associated with different reciprocal lattice vectors \({{\bf{g}}}{{=}}\left({n}_{x},{n}_{y},{n}_{z}\right)\frac{2\pi }{a}\), where \(a\) is the lattice constant of silicon. In contrast, the frequency of the classical CXR is solely determined by the longitudinal reciprocal lattice vectors labeled by \({n}_{z}\). Therefore, the quantum CXR peaks split and shift toward lower photon energies, as shown in (d) and (f). By increasing the electron energy, the multiple peaks gradually converge to coincide with the classically predicted peaks, as shown in (a) and (b). The electrons move along the \(z\) direction with kinetic energies of 5 MeV, 300 keV, and 30 keV.
