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题名	飞秒强激光场中的氢分子电离、解离及分子高次谐波研究
作者	彭鹏
学位类别	博士
答辩日期	2016
授予单位	中国科学院上海光学精密机械研究所
导师	李儒新
关键词	符合动量测量 分子电离 分子解离 高次谐波 分子取向
其他题名	Research on the ionization and dissociation of H2 and molecular high-order harmonic generation in intense femtosecond laser field
中文摘要	随着激光技术的快速发展，超短（飞秒）超强（拍瓦）激光脉冲得以实现。商品化的钛宝石啁啾脉冲放大激光系统可以轻易输出聚焦峰值光强高达1015 W/cm2的激光脉冲，其光电场强度已经可以与原子内部场强相比拟。如此强的激光脉冲作用于分子时，由于强烈的非线性作用会导致分子取向、定向、电离、解离、高次谐波产生、太赫兹辐射等诸多有趣现象。这些现象帮助我们解码出电子和原子核的超快动力学信息，这对人们认识微观世界具有重要意义。 本论文利用飞秒强激光脉冲，通过选择气态小分子，分别对分子电离、解离、高次谐波产生、无外场分子取向现象进行了研究。主要内容和创新点包括： 1、搭建了一套符合动量成像装置，该装置主要由超高真空系统、飞行时间谱仪、信号处理电路构成。我们对装置的各项参数（加速电压设置、模拟信号导出、模拟信号放大、模拟-数字信号转换、数字信号采集等）进行了仔细调试，利用商业化CoboldPC软件对离子信号进行了数据采集和分析，完成了离子-离子信号的符合动量测量。 2、利用我们搭建的符合动量成像装置，我们对H2分子的强场电离、解离现象进行了研究。利用泵浦-探测方案我们观测到了产生H+的两个解离通道和两个库仑爆炸通道，通过改变光强和延时，我们发现了两个库仑爆炸通道具有不同的光强依赖性和延时依赖性。利用两束40fs的激光脉冲在较近延时位置的干涉，我们研究了泵浦-探测实验中的干涉效应。我们观察到了质子动能谱受到的周期性调制，在不同的延时位置，发现了三种不同的调制形状，这些调制形状可以用干涉造成的激光脉冲包络的变化解释。 3、基于泵浦-探测方案，我们利用泵浦光对CO2分子进行预取向，然后引入更强的探测光产生高次谐波，我们在不同延时位置测量了高次谐波谱，发现了取向对高次谐波造成的频谱调制。通过对不同延时位置的高次谐波频谱信号的分析，我们对造成高次谐波频谱调制的两种机制进行了区分，一种来自于取向度的导数，另一种来自于取向导致的自由电子密度变化。 4、通过结合弱场偏振技术和平衡探测系统，我们提出了一种新的测量无外场分子取向度的方法。利用这种方法，我们对空气中N2分子和O2分子的取向进行了实验研究，通过一次测量，我们可以检测到瞬时取向的周期性重现结构、固有取向和碰撞造成的取向衰减。相比于现有的方法，我们的方法有可区分正、反取向、单次测量、不破坏取向分子的优势等诸多优势。
英文摘要	Benefited from the rapid development of laser technology, the ultrashort (femtosecond) and super strong (petawatt) laser pulse can be achieved. The commercial Ti: sapphire chirped pulse amplifier laser system can easily output femtosecond laser pulse with intensity higher than 1015W/cm2 after focusing, which means the strength of laser electric field becomes comparable to the Coulomb field of atom/molecule. When such a strong laser field is irradiated to molecules, the strong nonlinear interaction will induce a wealth of intersting phenomena including molecular alignment, orientation, ionization, dissociation, High-order harmonic generation (HHG) and Terahertz emission. These phenomena help us to decode the information of ultrafast dynamics of electrons and nuclei, which is very important for our understanding of the microworld. This thesis is based on femtosecond laser pulse, by choosing gaseous small molecules, we studied the molecular ionization, dissociation, HHG and field free molecular alignment. The main results and innovations are listed as follows: 1. We built a coincidence momentum imaging (CMI) system, which is mainly consisted of the ultra-high vacuum apparatus system, Time of flight mass spectrometer and the signal processing circuit. We tested the parameters of our system (acceleration voltage, derivation of analog signal, amplification of analog signal, conversion of analog-digital signal, acquisition of digital signal) carefully. By using the commercial software CoboldPC, we acquired and analysed the ion signal and completed the coincedence momentum measurement of ion-ion signal. 2. By using our CMI system, we studied the strong-field ionization and dissociation of H2. We observed two dissociation channels and two Coulomb explosion channels in pump-probe experiment of H2. By changing the pulse intensity and the time delay, we found these channels have different dependences on laser intensity and time delay. We also studied the interference effect in pump-probe experiment, by using two 40 femtoseconds laser pulses seperated by short time delay, the periodical modulation the measured H+ kinetic energy (KE) spectra was observed. We also found three different modulation shapes at different delay times, which can be explained by the pulse envelope change induced by the interference. 3. Based on the pump-probe scheme, we used the pump pulse to align the CO2 molecules, then the stronger, delayed probe pulse was induced to produce high-order harmonic. We measured the HHG at different delay times and found the spectra of high harmonics were modulated by molecular alignment. By analysing the spectra modulation at different delay times, we distinguished two effects contribute to the measured spectra modulation, one is from gradient of alignment degree and the other is plasma density varied by the molecular alignment. 4. By combining the weak field polarization technique (WFPT) with the balanced detection system, we proposed a new method for measuring the field free molecular alignment degree. The alignment behavior of N2 and O2 in air was studied experimentally by using this method. The periodic revival structures of the transient alignment, permanent alignment and collision-induced relaxation mechanism can be detected clearly by single measurement. Compared with the existing methods, our method has many advantages, such as: distinguishing between molecular alignment and anti-alignment, single measurement, does not destroy the aligned molecules.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15996]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	彭鹏. 飞秒强激光场中的氢分子电离、解离及分子高次谐波研究[D]. 中国科学院上海光学精密机械研究所. 2016.

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