Research Of The Generation And Characteristics Of The Novel Laser Pulse Based On The Time-lens System

With the increasing consumption of non-renewable energy,the energy problem has been paid more and more attention by all countries in the world.Nuclear fusion has attracted the attention of scientists because of its huge energy releasing,abundant raw fuel,clean and producing no pollution.Therefore,the best way to solve the current energy crisis is to study how to achieve controllable nuclear fusion.Laser inertial confinement fusion is one of the main ways to achieve controllable nuclear fusion.In order to achieve laser-driven nuclear fusion,researchers have proposed a variety of laser-driven nuclear fusion schemes,among which the central ignition method is widely adopted.Laser plasma instability(LPI)is one of the key factors affecting successful ignition of inertial confinement fusion(ICF)using central ignition.To that end,B.Afeyan et al.proposed to use STUD pulses(Spike train of uneven duration or delay pulses)to suppress LPI.Sub-pulses of STUD pulses are flat-topped pulses with specific targets,thus,how to obtain high-quality flat-topped pulses is the key to suppressing LPI using the STUD pulse scheme.The shock ignition scheme proposed by Betti et al.has become a new ignition scheme for inertial confinement fusion because of its advantages of low ignition energy threshold,high gain and better hydrodynamic stability.Shock pulse with high time precision and peak power contrast are the necessary condition for successful ignition.Therefore,controlling the pulse width and peak power contrast of shock pulse accurately is one of the important factors for final realization of shock ignition.In this thesis,to meet the requirements for specific time domain pulses with high quality,high precision and controllable in fusion,a novel time lens system based on cyclic phase modulation is proposed to numerically simulated high-precision controllable laser pulses,including STUD pulses,shock pulses and ultrashort pulses.The main research contents are as follows.By designing the initial super-Gaussian pulse,symmetrically quadratic phase modulation function and pulse compression system,a flattop pulse with pulse width of 2.8 ps,rising edge of 1.7 ps,spectral control accuracy of 0.1 nm and peak power fluctuation rate of less than 3% is realized based on the split-step Fourier algorithm.This kind of flat-top pulse,whose pulse width,rising edge and spectrum width can be actively controlled,is helpful to suppress the instability of laser plasma in laserdriven fusion process.By designing the initial sub-pulse waveform,asymmetric quadratic phase modulation function configuration and optimizing the pulse compression system,the shock pulse width and peak power contrast can be actively controlled separately.When adopting shock ignition method to realize fusion ignition,different devices and different physical properties require shock pulses have different parameters,so shock pulses with controllable pulse width and peak power contrast will have stronger adaptability.By offset carving an 11.77 ps Gaussian pulse,increasing phase modulation frequency and optimizing other system parameters,ultrashort pulses with pulse width of ~76 fs can be generated.The device can actively control the pulse width and rising edge of the output pulse,and overcome the shortcomings of the traditional passively mode-locked technology that can not adjust the performance parameters of ultra-short pulses.The time lens system proposed in this paper adopts non-mode-locked method to realize high-precision and controllable new pulse waveform.The structure of the system is simple and easy to operate.By optimizing the parameters of the time lens system,highly controllable STUD pulses,shock pulses and ultrashort pulses can be generated,which is important for realizing the special laser pulse waveforms needed in laser-driven inertial confinement fusion.