Investigation On Wavelength Scales Of High Order Harmonic Generation From He Atom Drived By Linear Polarization Pulse

The interaction between femtosecond pulsed intense laser and matter to produce high-order harmonic emission is one of the hot issues in the field of strong field physics.High harmonic emission has a wide range of applications in many aspects.It can be used as a low-cost XUV coherent light source.It is one of the effective means to obtain attosecond(10^-18s)light pulses.It can be used to detect complex molecular structures and dynamic processes.With the advancement of mid-infrared femtosecond pulsed laser technology,a new way for high-order harmonic generation is provided.In the process of high-order harmonic generation,driving the laser wavelength provides a convenient experimental control"knob".First,by controlling the Keldysh parameters and changing the ionization mechanism of electrons,it switches between the tunneling region and the multiphoton region.Second,the generation of high-order harmonics directly depends on the vibration energy of ionized electrons in the driving field,which can be pushed to an unprecedented high-energy limit by adjusting the wavelength.Third,by controlling the phase of higher harmonics by wavelength,there is hope to improve the generation of pulses in the attosecond region.In addition,the application of long-wave lasers is also very important for studying the generation of high-order harmonics in condensed phase systems,because it helps to generate high-conversion-efficiency harmonics in the transmission window of the material and increase the damage threshold.In this paper,by numerically solving the time-dependent Schr(?)dinger equation,the relationship between the intensity of the high-order harmonics generated by He under monochromatic linearly polarized pulse irradiation and the wavelength scale of the driving laser is systematically studied in theory.The study found that when the average kinetic energy Up(massive kinetic energy)of electrons remains unchanged in the limited driving field,the harmonic intensity decreases rapidly with the increase of the driving laser wavelength.Compared with the previous research work,the harmonic intensity-wavelength scaling law under certain conditions of the driving pulse light intensity,the harmonic intensity drops rapidly,and the scaling relationship has reached I_HH??^-13.Through comparative analysis of He atom ionization rate,ionization electron wave packet evolution,electron classical trajectory,and results in different spatial dimensions under different wavelength laser fields,it is found that under the condition of constant Up,the rapid decrease of harmonic intensity with the driving pulse wavelength is mainly attributed to Because the electron ionization rate decreases rapidly with the amplitude of the field strength(under certain conditions of Up,the increase of the wavelength will bring about the decrease of the field strength).There is also a part of the secondary reason that comes from the spatial dispersion effect of ionized electron wave packets.The higher the spatial dimension,the greater the influence of the dispersion effect(and in the case of a certain driving pulse light intensity,the effect of ionization changes with wavelength and the effect of spatial dispersion are comparable.match).The research work on the wavelength scale of atomic high-order harmonics in this thesis provides a useful reference and conclusion for people to control the efficiency of high-order harmonic emission.