Research On The Generation Mechanism Of Attosecond Light Pulses In The Interaction Of Ultra-strong, Ultra-short Lasers And Electrons

The attosecond light pulse is short-wavelength radiation with a very short pulse width.The use of the attosecond light pulse as the probe light can achieve ultra-high time resolution and has important potential applications in the fields of physics,chemistry,biology and medicine.At present,the generation of optical pulses of atoscray is mainly achieved by using laser and gas or solid interactions.High-order harmonics can be generated when the laser is interacting with a gas or a solid,and ultra-short pulses can be obtained after filtering the low-frequency components of the harmonics.With the development of laser technology,the electric field intensity of the laser has exceeded the relativistic intensity,and the free electron speed in the light field is close to the speed of light.According to the relativistic Doppler effect,the light waves radiated by the ultra-high-speed moving electrons can be extremely high.Due to the frequency component,it is possible to generate a attosecond optical pulse.Therefore,this dissertation focuses on the interaction between ultrashort laser pulses and free electrons,and analyzes the dynamic processes of electrons and the characteristics of ultra-high-speed electron radiation.1.The thesis discusses the dynamic theory of interaction between a strong laser field and free electrons and the theory of electron radiation.The thesis analyzes the model of laser field and electron interaction under classical approximation,and introduces the theory of electron radiation of covariant form of relativity theory,and gives a classical calculation method of the time and space distribution of electron radiation.2.The interaction between different intensity Gaussian beams and electrons whose pulse width is 15 fs is calculated,and the radiation of the attosecond pulse under corresponding conditions is studied.The results show that when the laser intensity is greater than the relativistic intensity,the electrons are mainly based on longitudinal motion,and the radiation is mainly concentrated on the longitudinal direction.Usually the radiation pulse is an atomic pulse train,but when the laser intensity is large such as a0=10,a single atomic pulse output with a pulse width of about 11 as is obtained.3.The role of the superposition field and free electrons in the combination of electrostatic field and Gaussian beam is studied.Firstly,the situation when the direction of the electrostatic field coincides with the direction of the laser polarization is calculated.It was found that when the electrostatic field strength increased to 5 ×10-4,a single attosecond pulse with a pulse width of 16 as was generated.The strength of the electrostatic field has less effect on the width of each atto-second pulse in the pulse train.Increasing the electrostatic field can effectively reduce the laser intensity threshold for generating a single attosecond optical pulse.The paper also calculated the situation where the electrostatic field is perpendicular to the polarization direction of the laser,and found that increasing the intensity of the electrostatic field does not yield the output of a single attosecond pulse.4.The interaction between the vortex light field and electrons of a circularly polarized Gaussian distribution is studied.The results show that the vortex beam converges on electrons,and the electrons initially distributed near the center of the spot all produce a velocity component that moves to the center of the spot.The pulse width of the electron radiation is only 2 as,and the direction of the radiation distribution is mainly in the direction of the last exit of the electron.Using a vortex beam reduces the intensity of the laser.In summary,this paper studied the effects of ordinary Gaussian,Gaussian and electric field superposition fields,and vortex Gaussian light field on free electrons.The electronic radiation pulses were analyzed.The use of superimposed fields and vortex fields reduced the generation of individual electrons.The intensity of the laser light required for the attosecond light pulse,in which the scheme using a vortex light field is more effective,the width of the attosecond pulse obtained is also smaller.