X-ray Production by Cascading Stages of a High-Gain Harmonic Generation Free-Electron Laser II: Special Topics

Abstract

In this paper, we study the tolerance of a new approach to produce coherent x-ray by cascading several stages of a High-Gain Harmonic Generation (HGHG) Free-Electron Laser (FEL). Being a harmonic generation process, a small noise in the initial fundamental signal will lead to a significant noise-to-signal (NTS) ratio in the final harmonic, so the noise issue is studied in this paper. We study two sources of noise: the incoherent undulator radiation, which is a noise with respect to the seed laser; and the noise of the seed laser itself. In reality, the electron beam longitudinal current profile is not uniform. Since the electron beam is the amplification medium for the FEL, this non- uniformity will induce phase error in the FEL. Therefore, this effect is studied. Phase error due to the wakefield and electron beam self-field is also studied. Synchrotronization of the electron beam and the seed laser is an important issue determining the success of the HGHG. We study the timing jitter induced frequency jitter in this paper. We also show that an HGHG FEL poses a less stringent requirement on the emittance than a SASE FEL does, due to a Natural Emittance Effect Reduction (NEER) mechanism. Thismore » NEER mechanism suggests a new operation mode, i.e., the HGHG FEL could adopt a high current, though unavoidable, a high emittance electron beam. Study in this paper shows that, production of hard x-rays with good longitudinal coherence by cascading stages of a HGHG FEL is promising. However, technical improvement is demanded.« less