Wakefield Generation By Chirped Laser Pulse In Inhomogeneous Plasma

The field of the ultrashort intense laser pulse interacts with the plasma has received great attention due to its wide application prospects.With the advent of chirped laser technology,an excellent chirped laser pulse has been used to interact with plasma more and more.Its rich physical phenomena have become the focus of discussion,especially,the research of wakefield when the chirped laser pulses propagating in the low density plasma.Many studies have shown that the interaction between the chirped laser pulse and the plasma can enhance the excitation of the wakefield.The effect of nonlinearly chirped laser pulse for wakefield excitation is better than that with the linear chirped laser pulse,which is due to the fact that the symmetry of the laser pulse is modified significantly for the nonlinearly chirped laser pulse.This pulse has a strong pondermotive force to burst through the electrons fully,and enhances the strength of the nonlinear wakefield.However,in the field of laser wakefield acceleration,obtaining a stronger wakefield has always been our goal.Considering the importance of plasma heterogeneity in the field of laser plasma,this paper focuses on the study of wakefield generation when the super Gaussian chirped laser pulse propagating in inhomogeneous plasma.In the first chapter,the development of laser plasma interaction,the interaction between ultrashort intense laser pulses and low-density plasma,and the application of plasma source are introduced briefly.The development of chirped laser pulses and the effect of chirped laser pulses on the excitation of the plasma wake are mainly described.The researches on the wakefield excitation which can be enhanced by the chirped laser pulses are introduced emphasically.In the second chapter,we discuss the effect of nonlinearly chirped superGaussian laser pulse on wakefield generation in an inhomogeneous plasma.The different types of nonlinearly chirped pulse are employed,and different kinds of inhomogeneous plasma density are used.The maximum wakefield amplitude as the function of nonlinearly chirped laser pulse and inhomogeneous plasma densityin parameter space are obtained.Moreover,the dependance of the maximum wakefield amplitude on the super-Gaussian laser pulse index is discussed.It shows that the larger wakefield can be obtained when the chirped pulse and inhomogeneous density are in the critical regions.Wakefield generation can be controlled by adjusting the chirped super-Gaussian pulse and inhomogeneous plasma density parameters.That is,we provide an efficient way for controlled generation of the wakefield.In the third chapter,the modulation of the amplitude and space structure of the plasma wakefield is studied.In our work,the different super Gaussian chirped laser pulse envelopes are used to strike the uniform and various inhomogeneous plasma.The researches show that,the chirped laser pulse can enhance the wakefield generation,make the bubbles structure transmutative seriously,reduce the numbers of bubbles in the same longitudinal distance,and enlarger the size of wakefield bubbles.Beside,the lager wakefield is gotten in inhomogeneous plasma compare to the uniform.And the effect of different density functions is diverse on wakefield generation,this due to its energetic gradient force.Moreover,the character of wakefield can be controlled by the two super Gaussian pulse index.And the choice of laser initial phase is meaningful to obtain a larger wakefield.Finally,we summarize the main results and give an outlook of the future in this field.