Coherent X-ray Sources Produced By Ultra-intense Ultra-short Laser

When relativistic laser pulses interact with gas or solid targets,electron bunches can be generated and accelerated to energy of MeV to GeV scale within ultra-short dis-tances.The length of these electron bunches is attoseconds to femtoseconds.Then the electron bunches oscillate in laser electrimagnetic field or field generated by plasma,leading to several kinds of coherent radiation sources,such as Thomson scattering source and XUV attosecond source.X-ray sources with very small size have spatial coherence and can be used for phase contrast imaging of light materials.X-ray sources with time coherence have very high brightness.Thomson scattering source with photon energy from several tens of keV to several MeV can be applied to phase contrast imaging of light materials,lossless detection of high Z materials,transient detection of femtosecond to picosecond physical process and nuclear resonance fluorescence stimulation of isotops.The coherent x-ray source with high brightness can be used in high-resolution material holography,ultrafast dynamic detection of organic materials,etc.Radiation sources driven by pulsed laser are natrually synchronized to the drive laser.So through combining the Thomson scattering source and attosecond source produced by the same laser facility,pumb-probe detecting method with attosecond temporal resolution can be ultilized,which acts as a very useful tool to the studies on the ultrafast electron dynamics in atom,the energy transformation process of hollow atoms to neighbouring atoms,and the damage mechanism of DNA molecules by ionizing radiation.Among them,the Thomson scattering light source with photon energy of tens of keV to several MeV can be applied to phase contrast imaging of light materials,non-destructive transmission detection of high-Z materials,transient process diagnosis of laser plasma interaction,detection of other femtosecond and picosecond scale ultrafast processes,and nuclear resonance fluorescence excitation of high-Z element isotopes,etc.Based on the Xingguang-? laser facility,SILEX-? femtosecond petawatt laser facility and 45TW femtosecond laser device in Laser Fusion Research Center,it is possible to establish an integrated ultrafast detection platform,which contains multi-ple ultrafast radiation sources with different parameters.Extreme ultraviolet radiation,soft X-ray,hard x-ray and gamma-ray radiation pulses with duration from several fem-toseconds to tens of attoseconds can be produced and precisely synchronized with each other.In order to achieve this goal,it is necessary to explore the relevant radiation mech-anism and carry out the necessary experimental studies.In this thesis,the study results on the all-optical Thomson scattering source based on laser wakefield acceleration,the coherent Thomson scattering source based on nano-target electron acceleration,and at-tosecond source based on high harmonic generation from solid,are introduced.For all-optical Thomson scattering light source,the optimization parameters which can be used to improve the monochromaticity and photon yield and reduce the emission angle,are explored using the Monte Carlo simulation tool.Through the experimental studies,it has been proved that the combined injection mechanism including ionization injection and shock wave front injection can greatly enhance the stability of electron injection.Through applying the combined injection to the cascade acceleration design,stable monoenergetic electron bunches with a central energy of 60 MeV can be gen-erated.Then plasma mirror is used to reflect the laser penetrating the jet target.The reflected laser interacts with the wakefield electron bunch,producing the signal of all-optical Thomson scattering light source.The energy spectra,photon yield and source size were diagnosed.In order to explore the ways to increase the photon yield of Thomson scattering source,the theory studies and numerical simulations of the coherent Thomson scatter-ing light source are conducted.A method to control the spatial distribution and energy of the relativistic electron mirror is proposed,which is realized by adjusting the inter-mediate spacing of the double-layer ultra-thin target.Resonance phenomenon between the relativistic electron mirror and the opposite moving laser is also found,which can be used to selectively enhance and suppress the radiation energy spectrum from the relativistic electron mirror.For the radiation mechanism of high-order harmonic generation from solid tar-get,numerical simulations on the interaction between strong relativistic laser and nano-target are conducted.Study results show that under the influence of the charge sepa-ration field from the target and the laser electromagnetic field,the trajectories of the electrons in the target can be described using a three-stage motion model.Based on this model,the electrons at different position of the target will be devided into several nanobunches,which will lead to attosecond pulse trains.Through adjusting the target length,the number of pulses in the trains can be controlled,Which reveals a method of generating isolated attosecond pulses based on multi-period pulse laser.