The free electron laser team of the Shanghai Advanced Research Institute of the Chinese Academy of Sciences has made important progress in the diagnosis of ultrafast free electron laser pulses. The team proposed and verified a new method for single-shot diagnosis of ultrafast free electron laser pulses based on self-reference interference spectroscopy, which provides a new idea for solving the problem of high-precision real-time diagnosis of attosecond free electron laser. The research results were published in Physical Review Letters, titled Self-Referenced Spectral Interferometry for Single-Shot Characterization of Ultrashort Free-Electron Laser Pulses.
To explore the basic processes of matter transformation in the microscopic world, such as photoelectric emission delay, valence electron motion, charge transfer, etc., advanced light sources with attosecond (10-18 second) time resolution capabilities are urgently needed. Attosecond light sources can be used to observe and manipulate the movement of electrons inside atoms and molecules, which helps scientists to explore chemical reactions, electronic structure, and molecular dynamics in greater depth, which is of great significance for materials science and chemical research. In recent years, important breakthroughs have been made in the physics and technology of X-ray free electron lasers, which have been able to generate attosecond X-ray pulses with extremely high peak brightness, which is expected to provide a revolutionary tool for attosecond scientific research. In addition to the generation of attosecond pulses, the complete time-frequency-domain information diagnosis of attosecond X-ray free electron laser is also important for ultrafast scientific experiments, and how to perform high-precision real-time diagnosis of this information has become a bottleneck limiting the application of attosecond X-ray free electron laser. In order to solve this problem, the team carried out systematic research work based on China’s free electron laser large scientific device.
In recent years, spectral phase interferometry (SPIDER) for direct electric field reconstruction has become one of the fast-growing pulse reconstruction methods in the field of ultrafast lasers. The key to this method is to generate a pair of replication pulses with the appropriate amount of spectral shear. This process generally requires the use of nonlinear crystalline materials, which makes it difficult to extend the method to short wavelengths. In this study, we innovatively propose to use the frequency traction effect of the free electron laser to generate spectral shear, and the ultrafast radiation pulse and the reference pulse are both generated by the same electron beam, so as to cleverly realize the self-reference spectral interference of the radiation pulse. The signal-to-noise ratio and efficiency of the reconstruction can be further improved by using the wavelet transform algorithm to improve the SPIDER, and the parameters of the Shanghai Soft X-ray Free Electron Laser Facility show that the complete time-frequency domain information of the attosecond X-ray pulse can be accurately reconstructed by this method (the reconstruction error is less than 6%). Compared with the ultrafast pulse diagnosis method in the traditional free electron laser device, this method has the advantages of simple equipment, high diagnostic efficiency (real-time, single shot), complete time-frequency domain information can be obtained at the same time, and the shorter the radiation pulse, the higher the diagnostic accuracy, which provides a new diagnostic method for the debugging and optimization of ultrafast X-ray free electron laser and attosecond scientific experiments based on X-ray free electron laser in the future.
The research work was supported by the National Natural Science Foundation of China and the Shanghai Youth Science and Technology Rising Star Program. (Source: Shanghai Advanced Research Institute, Chinese Academy of Sciences)
Related Paper Information:https://doi.org/10.1103/PhysRevLett.131.205002
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