强激光场下固体表面超快电子动力学及辐射机制研究进展

Research progress of ultrafast electron dynamics and radiation mechanisms on solid surfaces under intense laser fields

强激光固体等离子体相互作用可以驱动电子加速,电子的动力学过程具有亚光周期特性,可以激发阿秒电子脉冲.通过对电子空间图像的分析,可以反演激光固体等离子体相互作用的超快时间动力学.电子的发射伴随着电磁辐射的产生,如高次谐波X射线、太赫兹辐射等,辐射波段和固体靶的结构有着密切的联系.强激光能量向辐射能量的转化和电子与表面场的作用时间成正比,因此有效控制自由电子和表面场的相互作用可大大提高激光能量向辐射场的转化效率.基于Biermann电池效应、Weibel不稳定性等机制,通过激光驱动的强流电子可以在固体表面激发千特斯拉量级的强磁场,磁场演化的时间尺度在皮秒量级.本文从强激光和固体等离子体作用的超快(阿秒级)动力学开始,分析了电子流在飞秒以及皮秒时间尺度上的辐射特性,介绍了强磁场的产生及其演化的超快动力学.强激光和固体等离子体相互作用包含了丰富的内容,阿秒物理、辐射机制、实验室天体物理等领域还有待我们继续深入研究.

Intense laser-solid density plasma interaction can be studied on the attosecond,picosecond,and even nanosecond time scales.Laser-atom interactions and electron ionization in atoms and molecules occur on the attosecond time scales.Electrons can be accelerated in the interaction between a laser and solid-density plasma.The ultrafast dynamics of these electrons demonstrates sub-optical-cycle characteristics,leading to the excitation of attosecond electron pulse chains.By studying the attosecond electron dynamics,we can analyze the ultrafast dynamics in laser-solid density plasma interactions.Attosecond electrons can also be used to explore the ultrafast dynamics of electrons inside atoms,molecules,and condensed matter systems.By utilizing spatial streaking technology,we can separate attosecond electron pulse trains in space,thus generating isolated attosecond electron pulses.The ejection of electron beams is always accompanied with electromagnetic radiations,such as high harmonic generation(HHG)and terahertz radiation.The specific spectrum of this radiation is closely related to the detailed properties of the laser and the target material.As the scale lengths of the preplasma and laser intensity increase,the interaction turns chaotic.The space charge force at the surface of the solid density plasma should be taken into consideration.Attosecond electrons generated by mechanisms such as vacuum heating gradually disappear.On the picosecond and femtosecond time scales,electron emission can excite terahertz radiation.According to the basic working principles of a free electron radiation source,the intensity and energy conversion efficiency are limited by the duration of the interaction between free electrons and surface waves and the modulation distance.If longtime interaction between free electrons and surface waves can be achieved,it is theoretically possible to realize high energy conversion efficiency from free electrons to radiation.This miniaturized free electron light source operating in the terahertz range can be further extended to shorter wavelengths.By utilizing mechanisms such as the Biermann battery effect and Weibel instability,intense magnetic fields with kilotesla-level strength can be induced on the surface of the solid target.The time scale of the evolution of these magnetic fields is on the picosecond time scale.The Biermann battery effect and Weibel instability are closely related to the origin of cosmic magnetic fields.Motion of electrons in turbulent Weibel magnetic fields can excite Jitter radiation,which can cover X-ray and gamma-ray frequencies.Based on laser proton acceleration,collisionless shocks at or near relativistic velocity can be achieved.As the intensity of the laser reaches or approaches the order of 1023 W/cm2,the interaction between lasers and solid density plasma begins to be affected by the production of electron-positron pairs.Electron-positron pairs can be accelerated in the laser-solid density plasma interaction.Weibel instability driven by intense laser fields will be accompanied by the generation and annihilation of electron-positron pairs.This paper starts by examining the ultrafast(attosecond-level)dynamics of strong laser-solid plasma interactions,then analyzes the radiation characteristics of electron flow on attosecond and picosecond time scales,and finally introduces the ultrafast dynamics of the generation and evolution of strong magnetic fields.The interaction between strong lasers and solid density plasma encompasses various intriguing physical phenomena.Therefore,further research is needed in the fields of attosecond physics,radiation mechanisms,laboratory astrophysics,and other related areas.