飛秒激光誘導(dǎo)一氧化氮分子電離光電子速度成像研究
發(fā)布時(shí)間：2018-09-05 11:07
【摘要】：本論文以異核雙原子分子一氧化氮為例,通過速度成像技術(shù)在實(shí)驗(yàn)上探測了飛秒強(qiáng)激光場與分子作用電離產(chǎn)生的光電子速度成像,分析了激光光強(qiáng)對其共振激發(fā)電離路徑的影響,討論了其內(nèi)部的不同里德堡態(tài)在電離過程中的貢獻(xiàn),同時(shí)提取了相關(guān)里德堡態(tài)的角度分布特性信息。通過分析逸出電子的動(dòng)能和角度分布信息,為進(jìn)一步深入地理解分子的電離過程提供了實(shí)驗(yàn)依據(jù)。相對原子而言,分子的能級結(jié)構(gòu)更為復(fù)雜,在分子的電離解離過程研究中仍有很多現(xiàn)象還未得到準(zhǔn)確充分的解釋。為解決這些問題不僅需要發(fā)展更接近分子實(shí)際情況的理論模型,在實(shí)驗(yàn)技術(shù)手段上也要不斷的發(fā)展和創(chuàng)新。由此,本實(shí)驗(yàn)室搭建了六極桿裝置和電子速度成像裝置,分子束通過六極桿實(shí)現(xiàn)聚焦后與飛秒強(qiáng)激光場作用產(chǎn)生電子,再通過速度成像裝置對電子進(jìn)行速度成像探測。本文工作中提取并獲得了一氧化氮分子電離光電子的動(dòng)能分布及角度分布。在本論文的實(shí)驗(yàn)工作中對六極桿施加高壓的主要目的是將分子束聚焦以獲得更強(qiáng)的產(chǎn)物信號,實(shí)驗(yàn)中所使用的激光光源是線偏振800 nm和400 nm的飛秒激光,當(dāng)波長鎖定在800 nm時(shí),測量得到了不同激光光強(qiáng)(從1.1×10~（13） W/cm~2到7.8×10~（13） W/cm~2范圍內(nèi))的光電子速度成像,通過對光電子動(dòng)能譜結(jié)構(gòu)及其隨光強(qiáng)的通道切換現(xiàn)象進(jìn)行分析,將出現(xiàn)的共振峰全部進(jìn)行了歸屬,確定了在不同的光強(qiáng)作用下參與電離的里德堡態(tài),同時(shí)還獲得了電離過程中各里德堡態(tài)的逸出電子角度分布信息。當(dāng)激光波長為400 nm時(shí),測得了激光光強(qiáng)從2.0×10~（12）W/cm~2到1.4×10~（13）W/cm~2范圍內(nèi)的不同光強(qiáng)下光電子速度成像。與800 nm的光電子動(dòng)能譜不同,400 nm下的能譜結(jié)構(gòu)較單一,只存在一個(gè)較為清晰的共振峰及其對應(yīng)的ATI結(jié)構(gòu)。我們將800 nm出現(xiàn)的通道切換現(xiàn)象歸結(jié)為激光外場引起一氧化氮分子內(nèi)電子激發(fā)態(tài)能級的斯塔克移動(dòng),即隨著激光光強(qiáng)的改變在電離過程中共振電子激發(fā)態(tài)的貢獻(xiàn)也會(huì)發(fā)生變化,某特定電子激發(fā)態(tài)由于斯塔克效應(yīng)而正好步入多光子共振區(qū),導(dǎo)致動(dòng)能譜中對應(yīng)的峰值信號增強(qiáng);同時(shí)部分電子激發(fā)態(tài)則由于斯塔克移動(dòng)而逐漸遠(yuǎn)離多光子共振區(qū),所以對應(yīng)的峰值信號發(fā)生相應(yīng)減弱。進(jìn)一步通過對比不同激光光強(qiáng)下共振電離過程中各里德堡態(tài)所對應(yīng)的電子角度分布,我們發(fā)現(xiàn)電離光電子角度分布基本體現(xiàn)的是里德堡態(tài)的本質(zhì)屬性。一氧化氮分子光電子成像的實(shí)驗(yàn)探測研究,有助于我們對分子內(nèi)部里德堡態(tài)的結(jié)構(gòu)建立更全面的認(rèn)識(shí),更深入的理解一氧化氮分子的飛秒激光誘導(dǎo)共振增強(qiáng)多光子電離過程及過程中明顯的通道切換現(xiàn)象和電子角度分布,本論文工作中關(guān)于激光光強(qiáng)對分子電子激發(fā)態(tài)影響的分析,為實(shí)現(xiàn)強(qiáng)場下分子過程的量子調(diào)控提供了實(shí)驗(yàn)數(shù)據(jù)及相關(guān)依據(jù)。
[Abstract]:Taking the heteronuclear diatomic molecule nitric oxide as an example, the photoelectron velocity imaging produced by intense femtosecond laser field and molecular ionization is experimentally detected by velocity imaging technique in this thesis. The influence of laser intensity on the resonance excited ionization path is analyzed. The contribution of different Rydberg states in the process of ionization is discussed. The angular distribution characteristics of the related Rydberg states are also extracted. By analyzing the kinetic energy and angular distribution information of the escaping electrons, this paper provides an experimental basis for further understanding the ionization process of molecules. Compared with atoms, the energy level structure of molecules is more complex, and there are still many phenomena in the process of molecular ionization and dissociation that have not been fully explained. In order to solve these problems, it is necessary not only to develop theoretical models which are closer to the actual conditions of molecules, but also to develop and innovate the experimental techniques. Thus, a six-pole device and an electronic velocity imaging device are built in our laboratory. The molecular beam is focused through the six-pole rod to produce electrons after focusing with the femtosecond intense laser field, and then the velocity imaging device is used to detect the velocity of the electrons. The kinetic energy distribution and angular distribution of ionization photoelectron of nitric oxide have been obtained. The main purpose of applying high pressure to the hexpole rod in this paper is to focus the molecular beam to obtain a stronger product signal. The laser source used in the experiment is linearly polarized femtosecond laser of 800 nm and 400 nm, when the wavelength is locked at 800 nm. The photoelectron velocity imaging of different laser intensities (from 1.1 脳 10 ~ (13) W/cm~2 to 7.8 脳 10 ~ (13) W/cm~2) has been obtained. By analyzing the structure of the photoelectron kinetic energy spectrum and its channel switching with the light intensity, all the resonance peaks have been assigned. The Rydberg states which take part in ionization under different light intensities are determined, and the angle distribution information of the escape electrons of each Rydberg state in the process of ionization is also obtained. When the laser wavelength is 400 nm, the photoelectron velocities in the range from 2.0 脳 10 ~ (12) W/cm~2 to 1.4 脳 10 ~ (13) W/cm~2 have been measured. In contrast to the photoelectron kinetic energy spectrum of 800 nm, the spectral structure at 400 nm is relatively simple, and there is only one clear resonance peak and its corresponding ATI structure. The phenomenon of channel switching in 800 nm is attributed to the Stark shift of the excited state of the electron in the nitric oxide molecule caused by the external field of the laser, that is, the contribution of the resonant electron excited state to the ionization process will also change with the change of the intensity of the laser light. Due to the Stark effect, a certain excited state enters the multi-photon resonance region, which leads to the enhancement of the corresponding peak signal in the kinetic energy spectrum, while the partial excited state is gradually away from the multi-photon resonance region because of the Stark shift. So the corresponding peak signal weakens accordingly. Furthermore, by comparing the electron angular distributions of each Rydberg state in the process of resonance ionization under different laser intensities, we find that the angular distribution of ionization photoelectrons basically reflects the essential properties of the Rydberg state. The experimental investigation of nitric oxide photoelectron imaging will help us to establish a more comprehensive understanding of the structure of the Rydberg state within the molecule. A deeper understanding of the femtosecond laser-induced resonance enhanced multiphoton ionization process of nitric oxide and the obvious channel switching and electron angle distribution in the process is presented. In this work, the effect of laser intensity on the excited states of molecular electrons is analyzed. It provides experimental data and relevant basis for realizing quantum regulation of molecular process in strong field.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O561
本文編號：2224085
[Abstract]:Taking the heteronuclear diatomic molecule nitric oxide as an example, the photoelectron velocity imaging produced by intense femtosecond laser field and molecular ionization is experimentally detected by velocity imaging technique in this thesis. The influence of laser intensity on the resonance excited ionization path is analyzed. The contribution of different Rydberg states in the process of ionization is discussed. The angular distribution characteristics of the related Rydberg states are also extracted. By analyzing the kinetic energy and angular distribution information of the escaping electrons, this paper provides an experimental basis for further understanding the ionization process of molecules. Compared with atoms, the energy level structure of molecules is more complex, and there are still many phenomena in the process of molecular ionization and dissociation that have not been fully explained. In order to solve these problems, it is necessary not only to develop theoretical models which are closer to the actual conditions of molecules, but also to develop and innovate the experimental techniques. Thus, a six-pole device and an electronic velocity imaging device are built in our laboratory. The molecular beam is focused through the six-pole rod to produce electrons after focusing with the femtosecond intense laser field, and then the velocity imaging device is used to detect the velocity of the electrons. The kinetic energy distribution and angular distribution of ionization photoelectron of nitric oxide have been obtained. The main purpose of applying high pressure to the hexpole rod in this paper is to focus the molecular beam to obtain a stronger product signal. The laser source used in the experiment is linearly polarized femtosecond laser of 800 nm and 400 nm, when the wavelength is locked at 800 nm. The photoelectron velocity imaging of different laser intensities (from 1.1 脳 10 ~ (13) W/cm~2 to 7.8 脳 10 ~ (13) W/cm~2) has been obtained. By analyzing the structure of the photoelectron kinetic energy spectrum and its channel switching with the light intensity, all the resonance peaks have been assigned. The Rydberg states which take part in ionization under different light intensities are determined, and the angle distribution information of the escape electrons of each Rydberg state in the process of ionization is also obtained. When the laser wavelength is 400 nm, the photoelectron velocities in the range from 2.0 脳 10 ~ (12) W/cm~2 to 1.4 脳 10 ~ (13) W/cm~2 have been measured. In contrast to the photoelectron kinetic energy spectrum of 800 nm, the spectral structure at 400 nm is relatively simple, and there is only one clear resonance peak and its corresponding ATI structure. The phenomenon of channel switching in 800 nm is attributed to the Stark shift of the excited state of the electron in the nitric oxide molecule caused by the external field of the laser, that is, the contribution of the resonant electron excited state to the ionization process will also change with the change of the intensity of the laser light. Due to the Stark effect, a certain excited state enters the multi-photon resonance region, which leads to the enhancement of the corresponding peak signal in the kinetic energy spectrum, while the partial excited state is gradually away from the multi-photon resonance region because of the Stark shift. So the corresponding peak signal weakens accordingly. Furthermore, by comparing the electron angular distributions of each Rydberg state in the process of resonance ionization under different laser intensities, we find that the angular distribution of ionization photoelectrons basically reflects the essential properties of the Rydberg state. The experimental investigation of nitric oxide photoelectron imaging will help us to establish a more comprehensive understanding of the structure of the Rydberg state within the molecule. A deeper understanding of the femtosecond laser-induced resonance enhanced multiphoton ionization process of nitric oxide and the obvious channel switching and electron angle distribution in the process is presented. In this work, the effect of laser intensity on the excited states of molecular electrons is analyzed. It provides experimental data and relevant basis for realizing quantum regulation of molecular process in strong field.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：O561
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