Atomic Inner-shell Radiation Seeded X-ray Free-electron Lasers

X-ray free electron laser(XFEL)can generate short-wavelength radiation pulses with high power,good transverse coherence and continuously adjustable wavelength.These characters make XFELs have a wide range of applications in many fields such as atomic physics,nanomaterial science,femtosecond chemistry,and biomolecular structure.At present,the self-amplification spontaneous emission(SASE)operation mode is usually adopted as the main operation scheme of the XFELs.This mode maintains the advantages of simple structure and adjustable wavelength,but the longitudinal coherence of the output radiation pulse becomes poor due to the noise start-up effect of its own electron beam.In order to improve the longitudinal coherence of XFELs,a number of improved operating modes have been proposed.Among them,the high-gain high-harmonic amplification(HGHG)operation mode and the selfseeding operation mode are the most mature and are confirmed by experiments.However,the HGHG operation mode with external seeds is limited,where the large energy dispersion of the electron beam affects the conversion efficiency of higher harmonics,resulting in the difficulty to keep the output pulse quality when applied to XFELs.In another seed operation mode,the first part of the SASE jitter also causes output pulse instability.Recently,with the development of X-ray free electron laser devices,atomic inner shell lasers have been experimentally realized.By using high-power and short-pulsed XFEL to pump the inner shell electrons of specific atoms,this method can produce a X-ray laser with enhanced coherence.Therefore,attempting to introduce an inner-shell laser-related mechanism into existing XFEL devices may provide a new idea for achieving coherent x-ray pulsed beams with high-quality.This thesis aims to improve the longitudinal coherence of X-ray free-electron lasers.By combining the atomic inner shell laser with the self-seed operating mode,an atomic inner shell laser is proposed as a seed-driven XFEL operating mode.In this mode,SASE XFEL is utilized as a pumping source to pump neutral atoms,and then the generated inner shell laser is suggested as a seed laser to modulate electron bunches to produce a fully coherent free electron laser.The discussion of the thesis can be summarized by the two steps.Firstly,based on the semi-classical laser theory,the rate equations of the number of occupied energy levels in the inner shell of the selected atom are derived,and the Gaussian type of XFEL is utilized as the pump source to study the generation mechanism of the inner shell laser.It is shown that this scheme can produce high-power of atomic inner shell lasers,thus,can be used as the seed lasers for subsequent XFEL modulated electron beams.Secondly,based on the design parameters of Shanghai Coherent Light Source,the fresh-slice technique is adopted to simulate the start-to-end process of the model.The simulation generates high-power of X-ray output pulses up to 210 GW,with the pulse width 0.58 e V and a time bandwidth product 1.02.The results exhibit the possibility of such a scheme to produce a XFEL with high-power,short-pulse,and short-wavelength,as well as fully transverse and longitudinal coherence.Relevant design and theoretical simulations confirm the feasibility of X-ray free electron laser driven by the atomically inner shell radiation,and provide a possible design scheme for Shanghai Coherent Light Sources to produce short pulse radiation(soft X-ray,hard X-ray,etc.)with high-quality and full coherence.