Enhancement of free-electron coherent harmonic generation by use of the dispersive function on a storage ring

An alternative to the free-electron laser (FEL) oscillator at short wavelengths (λ<2000 Å) is the coherent harmonic generation (CHG) process; the electron beam, when passing through the undulator, acts as a nonlinear medium and allows one to obtain coherent harmonics of an external laser. However, this coherent emission is rather weak, particularly on the high-order harmonics (n⩾5). It is shown that the introduction of an energy dispersive function on a storage ring decreases the local energy spread of the beam and then increases the CHG by several orders of magnitude