Research progress of ultrafast electron dynamics and radiation mechanisms on solid surfaces under intense laser fields
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 long-time 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 1023W/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.
attosecond dynamicsultrafast electron pulseintense terahertz radiationsintense magnetic field
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