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[ Instrument R & D of Instrument Network ] Recently, the research group of laser-induced ultrafast electron dynamics at the Institute of Precision Measurement Science and Technology Innovation, Chinese Academy of Sciences has made new progress in the study of physical models, found the law of ultrafast dynamics of electrons in liquids, and developed Concise equation. The equation organically combines the distribution of atoms in the liquid, the parameters of the laser, and the photons of radiated harmonics. The predicted maximum harmonic photon energy is completely consistent with the experimental measurement results. The research results were recently published in Phys. Rev. Lett.
High-order harmonics refer to a series of high-frequency coherent waves radiated by the non-linear interaction of a low-frequency strong field ultrafast laser and matter. Among them, the research on the higher harmonics generated by the interaction between laser and gas is relatively thorough, and it is also the main method for generating attosecond lasers. However, the low efficiency of gas harmonic generation is the main factor restricting its application. With the development of long-wave infrared-driven lasers, scientists have found that crystals can also generate nonlinear higher-order harmonics. Due to their high density and good internal atom arrangement regularity, they are expected to achieve compact and high conversion efficiency of higher-order harmonic sources . However, the laser damage threshold that most crystals can withstand is relatively low, making it difficult to produce high-energy photons. Liquid higher harmonics combine the advantages of some solid and gas harmonics. The sample has the characteristics of high density, and can withstand high driving light intensity, low cost, easy to prepare and update, which is a new direction for future development. At present, scientists' understanding of the mechanism of liquid higher harmonics has always been blank, and theoretical breakthroughs are urgently needed.
The Laser Induced Ultrafast Electron Dynamics Research Group of the Institute of Precision Measurement has been focusing on the study of higher harmonic theory, and has made a series of influential results in the field of gas and solid higher harmonics. Faced with the problem of microscopically complex and disordered liquid systems, they developed a set of physical models using statistical methods. After a large number of numerical simulations combined with physical principles, they found the laws of ultrafast dynamics of electrons in liquids. The new equations developed include The interaction between microscopic electrons and strong lasers is fully considered, and the macroscopic statistical distribution of atoms is fully considered. Not only the obtained harmonic spectrum characteristics are qualitatively consistent with the experimental results, but also the predicted maximum harmonic photon energy and experimental measurement results Quantitative compliance. After the manuscript Zeng Aiwu, the first author of the thesis, and Bian Xuebin, the corresponding author researcher, the three reviewers unanimously gave a high evaluation, thinking that the theoretical model is groundbreaking and is the first theoretical model in the field of liquid harmonics , Revealing the profound relationship between the macroscopic statistics of structural fluctuations and the odd-even transition and truncation energy of the harmonic spectrum, which will provide guidance for the development of related experiments.
This research work was supported by the National Natural Science Foundation of China's major research project "New Light Field Control Physics and Applications".