Higher Harmonic in Free Electron Laser with Combined Electromagnetic Wiggler and Axial Guide Magnetic Fields

Following a single-particle approach, a detailed analysis of the higher harmonic in free electron laser (FEL) with combined electromagnetic wiggler and axial guide magnetic fields is derived. The spontaneous emission spectrum and the gain in the low-gain Compton regime are also calculated in detail. This analysis results in a clear resonance condition and shows that this kind of FEL can generate significant coherent harmonic emission of radiation with axial guide magnetic field of suitable strength.