Synchrotron radiation stability with meV-level energy resolution: in situ characterization

One of the most critical parameters in synchrotron radiation (SR) experiments is the stability of the photon energy, which is primarily affected by the stability of the light source and the optical elements in the beamline. Due to the characteristics of SR and the use of dispersive elements such as monochromators in the beamline, the change of the beam position is usually accompanied by the change of energy and flux, while most traditional beam monitoring methods are based on the direct or indirect measurement of total flux, and are therefore sensitive to the beam position only, having no energy resolution. In this paper, an in situ monitoring system has been designed to measure the short-term (jitter) and long-term (drift) characteristics of the energy variation in the SR beamline. The system consists of a double-crystal monochromator, an orthogonal analysis crystal, and an X-ray imaging detector, which could decouple the angle and energy spread of the photon beam based on the dispersion effect in Bragg diffraction. The time response and the energy resolution of the system could reach millisecond and millielectron volt level, respectively.