原子在強激光場中的電離
發(fā)布時間：2019-06-24 17:45
【摘要】：隨著超短超強激光技術(shù)的快速發(fā)展,激光與原子相互作用的研究引起了人們的廣泛關(guān)注。人們觀察到了高次諧波發(fā)射(HHG),閾上電離(ATI),非序列雙電子電離(NSDI)等強場物理現(xiàn)象。由于原子在強激光場中的電離是一切后續(xù)物理過程的基礎(chǔ),因此對原子的電離研究具有重要意義。所以,我們從理論上分別研究了原子在強激光脈沖作用下的閾上電離過程和雙電離過程。具體研究工作包括以下內(nèi)容:第一,我們通過求解單電子原子的一維含時薛定諤方程研究ATI過程。我們研究了一維長程勢和短程勢對電離譜平臺結(jié)構(gòu)的影響。發(fā)現(xiàn)在相同入射激光強度下,長程勢下電離譜呈現(xiàn)出清晰的雙平臺結(jié)構(gòu);而短程勢下電離譜雙平臺強度差明顯小于長程勢下的雙平臺強度差。并且,隨著入射激光強度的減小,短程勢下雙平臺結(jié)構(gòu)逐漸變成單平臺結(jié)構(gòu)。我們通過量子模擬和經(jīng)典分析,闡明了不同模型勢下平臺結(jié)構(gòu)出現(xiàn)差異的原因:在相同入射激光強度下,短程勢下電子電離幾率小于長程勢下的電離幾率;在相同電離幾率情況下,短程勢的重散射截面大于長程勢的重散射截面。第二,我們利用動量空間含時偽譜方法求解單電子原子的三維含時薛定諤方程研究ATI過程。首先研究了高頻激光脈沖與激發(fā)態(tài)原子相互作用的光電離過程。通過計算電離閾值附近光電子能譜和動量角分布譜,發(fā)現(xiàn)體系初態(tài)波函數(shù)的主量子數(shù)可以由光電子能譜的第一個峰值位置來確定,體系初態(tài)波函數(shù)的角量子數(shù)可以由光電子動量角分布譜來確定。我們通過變化激光參數(shù),發(fā)現(xiàn)這一規(guī)律不隨入射激光強度和脈寬的改變而改變。因此我們可以利用高頻激光脈沖中原子的電離信號對原子初態(tài)波函數(shù)進行標(biāo)定。我們的方法為研究原子初態(tài)波函數(shù)成像問題提供了一種新方案。其次我們討論了不同入射激光強度下的光電子譜,發(fā)現(xiàn)隨入射激光強度的增加每個ATI峰由單峰變?yōu)槎喾?如果繼續(xù)增加入射激光強度,每個ATI峰再次變?yōu)閱畏褰Y(jié)構(gòu)。上述計算結(jié)果與相應(yīng)的實驗測量結(jié)果符合很好。通過對原子束縛態(tài)布居分析,我們發(fā)現(xiàn)束縛態(tài)多光子激發(fā)導(dǎo)致上述現(xiàn)象的發(fā)生。最后我們討論了在Freeman共振條件下,光電子能譜和光電子角分布與入射激光強度和激光脈沖的載波包絡(luò)相位(CEP)的依賴關(guān)系。我們發(fā)現(xiàn)從基態(tài)直接電離的電子,ATI峰值位置隨入射激光脈沖強度的增加移動一個pU(pU為有質(zhì)動力能),從較高激發(fā)態(tài)電離的電子,ATI峰值位置隨入射激光脈沖強度的增加不移動。原因如下:從基態(tài)直接電離的電子,由于基態(tài)具有較大的電離勢,能級移動較小,而末態(tài)能級移動pU,所以ATI峰值位置隨激光脈沖強度的增加而移動。而從較高激發(fā)態(tài)電離的電子,初態(tài)和末態(tài)能級在激光場作用下移動相同的pU,因此ATI峰值位置不會隨著激光脈沖強度的增加而移動。此外,我們研究激光脈沖的CEP對光電子能譜的影響。發(fā)現(xiàn)在光電子能譜Freeman共振位置附近,光電子的電離幾率隨激光脈沖的CEP改變而改變。通過分析每個分波對光電子譜的貢獻,我們可以確定影響光電子譜強度的分波。通過利用光電子角分布信息,我們能提供一種探測多周期激光脈沖CEP的新方案。第三,我們基于B樣條理論求解雙電子原子滿足的含時薛定諤方程,研究了氦原子在深紫外(XUV)激光脈沖作用下的雙光子雙電離過程。首先我們檢驗計算方法在強XUV激光脈沖作用下的有效性。其次研究了激光脈沖寬度對電離電子能譜結(jié)構(gòu)的影響。發(fā)現(xiàn)能量譜結(jié)構(gòu)隨脈沖寬度的增加由單峰變成雙峰。通過對長脈沖下雙電子電離動力學(xué)過程的分析,我們發(fā)現(xiàn)雙電子在電離過程中的相互作用形成雙峰結(jié)構(gòu)。最后我們討論了氦原子激發(fā)態(tài)1S2S和1S2P態(tài)作為初態(tài)時的電離過程。
[Abstract]:With the rapid development of the ultra-short and super-intense laser technology, the study of the interaction of the laser and the atoms has attracted a wide range of attention. The physical phenomena of high-order harmonic emission (HHG), suprathreshold ionization (ATI) and non-sequence double electron ionization (NSDI) were observed. The ionization of atoms in the strong laser field is the basis of all follow-up physical processes, so it is of great significance to study the ionization of atoms. So, we theoretically study the ionization process and the double ionization process of the atoms under the action of strong laser pulse. The specific research work includes the following: first, we study the ATI process by solving the one-dimensional time-time Schrodinger equation of the single electron atom. We have studied the effect of one-dimensional long-range potential and short-range potential on the structure of the platform. It is found that under the same incident laser intensity, a clear double-platform structure is displayed under the long-range potential, and the strength difference of the double-platform under the short-range potential is obviously smaller than that of the double-platform under the long-range potential. Moreover, with the decrease of the incident laser intensity, the double-platform structure gradually becomes a single-platform structure under the short-range potential. Through the quantum simulation and the classical analysis, the reason of the difference of the platform structure under the different model potential is explained: under the same incident laser intensity, the electron ionization probability under the short-range potential is less than the ionization probability under the long-range potential; and in the case of the same ionization probability, The cross section of the short-range potential is larger than the heavy-scattering cross-section of the long-range potential. Secondly, we use the momentum space-time pseudospectral method to solve the three-dimensional time-time Schrodinger equation of the single electron atom to study the ATI process. The photoionization process of the interaction between the high-frequency laser pulse and the excited-state atom is studied. The main quantum number of the initial state wave function of the system can be determined by the first peak position of the photoelectron spectrum by calculating the photoelectron spectrum and the momentum angular distribution spectrum near the ionization threshold, and the angle quantum number of the initial state wave function of the system can be determined by the photoelectron momentum angular distribution spectrum. By changing the laser parameters, we find that this rule does not change with the change of the intensity of the incident laser and the pulse width. So we can use the ionization signal of the atom in the high-frequency laser pulse to calibrate the atomic initial state wave function. Our method provides a new scheme for studying the imaging of the first-state wave function of the atom. Second, we discussed the photoelectron spectrum of different incident laser intensity, and found that each ATI peak changed from single peak to multi-peak with the increase of incident laser intensity, and if the incident laser intensity was continued to increase, each ATI peak again became a unimodal structure. The results of the above calculation are in good agreement with the corresponding experimental results. By analyzing the bound state of the atom, we find that the bound-state multi-photon excitation leads to the above-mentioned phenomenon. Finally, we discuss the dependence of the photoelectron spectrum and the photoelectronic angular distribution on the carrier envelope phase (CEP) of the incident laser intensity and the laser pulse under the Freeman resonance condition. We find that the peak position of ATI moves with the increase of the intensity of the incident laser pulse with the increase of the intensity of the incident laser pulse, and the peak position of ATI does not move with the increase of the intensity of the incident laser pulse. The reason is as follows: the electrons that are directly ionized from the ground state, because the ground state has a large ionization potential, the energy level moves smaller, and the last energy level moves the pU, so the peak position of the ATI moves with the increase of the laser pulse intensity. And the electron, the initial state and the final state energy level ionized from the higher excited state move the same pU under the action of the laser field, so the peak position of the ATI does not move with the increase of the laser pulse intensity. In addition, we study the effect of the CEP of the laser pulse on the photoelectron spectroscopy. It was found that in the vicinity of the Freeman resonance position of the photoelectron spectroscopy, the probability of ionization of the photoelectrons changes with the change of the CEP of the laser pulse. By analyzing the contribution of each wave to the photoelectron spectrum, we can determine the distribution of the intensity of the photoelectron spectrum. By using the optoelectronic angular distribution information, we can provide a new scheme for detecting a multi-period laser pulse CEP. Thirdly, we study the two-photon double ionization process under the action of deep ultraviolet (XUV) laser pulse by using the B-spline theory to solve the time-dependent Schrodinger equation. First, we verify the effectiveness of the calculation method under the strong XUV laser pulse. Secondly, the effect of laser pulse width on the structure of ionization electron energy spectrum is studied. It was found that the energy spectrum structure changed from single peak to double peak with the increase of the pulse width. Through the analysis of the dynamic process of double electron ionization under long pulse, we find that the interaction of the two electrons in the ionization process forms a double-peak structure. Finally, we discuss the ionization process of the states of the excited states of the helium atom and the state of the 1S2P as the initial state.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：O562
本文編號：2505244
[Abstract]:With the rapid development of the ultra-short and super-intense laser technology, the study of the interaction of the laser and the atoms has attracted a wide range of attention. The physical phenomena of high-order harmonic emission (HHG), suprathreshold ionization (ATI) and non-sequence double electron ionization (NSDI) were observed. The ionization of atoms in the strong laser field is the basis of all follow-up physical processes, so it is of great significance to study the ionization of atoms. So, we theoretically study the ionization process and the double ionization process of the atoms under the action of strong laser pulse. The specific research work includes the following: first, we study the ATI process by solving the one-dimensional time-time Schrodinger equation of the single electron atom. We have studied the effect of one-dimensional long-range potential and short-range potential on the structure of the platform. It is found that under the same incident laser intensity, a clear double-platform structure is displayed under the long-range potential, and the strength difference of the double-platform under the short-range potential is obviously smaller than that of the double-platform under the long-range potential. Moreover, with the decrease of the incident laser intensity, the double-platform structure gradually becomes a single-platform structure under the short-range potential. Through the quantum simulation and the classical analysis, the reason of the difference of the platform structure under the different model potential is explained: under the same incident laser intensity, the electron ionization probability under the short-range potential is less than the ionization probability under the long-range potential; and in the case of the same ionization probability, The cross section of the short-range potential is larger than the heavy-scattering cross-section of the long-range potential. Secondly, we use the momentum space-time pseudospectral method to solve the three-dimensional time-time Schrodinger equation of the single electron atom to study the ATI process. The photoionization process of the interaction between the high-frequency laser pulse and the excited-state atom is studied. The main quantum number of the initial state wave function of the system can be determined by the first peak position of the photoelectron spectrum by calculating the photoelectron spectrum and the momentum angular distribution spectrum near the ionization threshold, and the angle quantum number of the initial state wave function of the system can be determined by the photoelectron momentum angular distribution spectrum. By changing the laser parameters, we find that this rule does not change with the change of the intensity of the incident laser and the pulse width. So we can use the ionization signal of the atom in the high-frequency laser pulse to calibrate the atomic initial state wave function. Our method provides a new scheme for studying the imaging of the first-state wave function of the atom. Second, we discussed the photoelectron spectrum of different incident laser intensity, and found that each ATI peak changed from single peak to multi-peak with the increase of incident laser intensity, and if the incident laser intensity was continued to increase, each ATI peak again became a unimodal structure. The results of the above calculation are in good agreement with the corresponding experimental results. By analyzing the bound state of the atom, we find that the bound-state multi-photon excitation leads to the above-mentioned phenomenon. Finally, we discuss the dependence of the photoelectron spectrum and the photoelectronic angular distribution on the carrier envelope phase (CEP) of the incident laser intensity and the laser pulse under the Freeman resonance condition. We find that the peak position of ATI moves with the increase of the intensity of the incident laser pulse with the increase of the intensity of the incident laser pulse, and the peak position of ATI does not move with the increase of the intensity of the incident laser pulse. The reason is as follows: the electrons that are directly ionized from the ground state, because the ground state has a large ionization potential, the energy level moves smaller, and the last energy level moves the pU, so the peak position of the ATI moves with the increase of the laser pulse intensity. And the electron, the initial state and the final state energy level ionized from the higher excited state move the same pU under the action of the laser field, so the peak position of the ATI does not move with the increase of the laser pulse intensity. In addition, we study the effect of the CEP of the laser pulse on the photoelectron spectroscopy. It was found that in the vicinity of the Freeman resonance position of the photoelectron spectroscopy, the probability of ionization of the photoelectrons changes with the change of the CEP of the laser pulse. By analyzing the contribution of each wave to the photoelectron spectrum, we can determine the distribution of the intensity of the photoelectron spectrum. By using the optoelectronic angular distribution information, we can provide a new scheme for detecting a multi-period laser pulse CEP. Thirdly, we study the two-photon double ionization process under the action of deep ultraviolet (XUV) laser pulse by using the B-spline theory to solve the time-dependent Schrodinger equation. First, we verify the effectiveness of the calculation method under the strong XUV laser pulse. Secondly, the effect of laser pulse width on the structure of ionization electron energy spectrum is studied. It was found that the energy spectrum structure changed from single peak to double peak with the increase of the pulse width. Through the analysis of the dynamic process of double electron ionization under long pulse, we find that the interaction of the two electrons in the ionization process forms a double-peak structure. Finally, we discuss the ionization process of the states of the excited states of the helium atom and the state of the 1S2P as the initial state.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：O562
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