Suppressing of even harmonics in free electron lasers by modifying the energy spread of the beam

Abstract

Using an analytical description of the evolution of the power of harmonics in free electron laser (FEL) undulators, we study the effect of electron beam parameters on the main characteristics of FEL radiation: the gain length, spectrum, and harmonic power. The possibility of suppressing even harmonics of the FEL as a light source in the study of materials and surfaces by analyzing the second harmonic nonlinear response (SHG) is being studied. The main factors influencing the radiation of even FEL harmonics are revealed; the influence of the beam cross section and the spread of electron energies on their radiation is analyzed. An example of a LEUTL FEL with visible light emission, which is used in studies of the optical properties of materials and the chemical state of molecules on surfaces and interfaces between media, is considered. In this context, the possibility of suppressing the second FEL harmonic is analyzed.