Real time measurement of femtosecond dynamics of relativistic intense laser driven ultra-hot electron beams

In the interaction between ultra short and ultra strong laser and matter, electrons with short pulse width and high energy are generated, commonly referred to as "hot electrons". The generation and transport of hot electrons is one of the important fundamental issues in high-energy density physics of lasers. Superhot electrons can excite a wide range of ultrafast electromagnetic radiation, as well as drive ion acceleration and rapid heating of matter, serving as energy carriers in the "fast fire" process of inertial confinement fusion. The properties of various secondary radiation and particle sources, plasma heating and energy deposition processes are closely related to the temporal, spatial, and energy characteristics, as well as the evolution dynamics of hot electrons.

After years of research, people have gained a clear understanding of the energy and spatial characteristics of superheat electrons. However, due to the lack of suitable high-resolution measurement methods, the diagnosis of the time structure and dynamic processes of superheat electron beams still faces challenges.

Liao Guoqian, a distinguished researcher of the Institute of Physics of the Chinese Academy of Sciences/Key Laboratory of Photophysics of the National Research Center for Condensed Matter Physics in Beijing, Li Yutong, a researcher, and Zhang Jie, an academician of the CAS Member, have explored for many years a new way to generate high power terahertz radiation from the interaction between ultra intense lasers and solid targets, proposed a terahertz generation model based on the coherent transition radiation of ultra hot electron beams, and developed a single shot ultra wideband terahertz detection technology based on non collinear autocorrelation.

Based on the above achievements, researchers have recently proposed a new method for diagnosing superheat electron beams using terahertz radiation. Using a self-developed high time resolution single shot terahertz autocorrelation instrument, in-situ and real-time measurements of the time-domain structure and dynamics of superheat electron beams during the interaction between ultra strong lasers and thin film targets have been achieved.

This study theoretically constructs a mapping relationship between terahertz radiation properties and the spatiotemporal characteristics of superheat electron beams, and provides a quantitative relationship between terahertz pulse width and parameters such as electron beam pulse width, beam spot size, and emission angle. This study accurately characterized the pulse width of a few tens of femtoseconds level hot electron beam in the laser solid target interaction. It was found that the electron beam accelerated by the ultra strong laser has a pulse width similar to that of the driving laser during generation. During transmission, the longitudinal time width and transverse spatial size gradually widen due to velocity dispersion and angular divergence; We directly observed the dynamics of hot electron backflow caused by secondary acceleration of laser pulses and target surface sheath field. It was found that when a high contrast laser interacts with a thin film target, the electron beam bounces back and forth between the front and back surface sheath fields of the target, with a duration of up to 100 femtoseconds. These results demonstrate single shot, non-destructive, in situ, and high temporal resolution methods for characterizing hot electrons, which contribute to understanding and optimizing the spatiotemporal characteristics of ultrafast radiation and particle sources based on hot electrons, and developing related applications.

Diagnosis of pulse width of superheat electron beam using terahertz coherent transition radiation

Diagnosis of Superhot Electron Reflux Dynamics Based on Multi cycle Terahertz Pulses

The related achievements are titled Femtosecond dynamics of fast electron pulses in related laser oil interactions and published in the Physical Review Letters. The research work was supported by the National Natural Science Foundation of China, the Ministry of Science and Technology and the Chinese Academy of Sciences.

Paper link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.155001

Source: Institute of Physics