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题名	强场电离诱导产生空气激光光谱学研究
作者	张海粟
学位类别	博士
答辩日期	2014
授予单位	中国科学院上海光学精密机械研究所
导师	程亚
关键词	隧穿电离 分子转动波包 飞秒激光成丝 空气激光。
其他题名	Air-Laser Spectroscopy Induced by Strong Field Ionization
中文摘要	强场物理是当今物理学研究的重要前沿领域。近些年来，超快激光技术的迅速发展使人们获得了脉宽更短、能量更高、覆盖波段更宽的激光光源，从而使强激光与物质相互作用的研究从传统的微扰区域推进到非微扰区域。 在如此高强度的激光照射下，原子分子会产生一系列新奇的现象，包括高次谐波辐射，阈上电离和解离，分子键的硬化和软化，库伦爆炸，分子取向和转动波包，粒子数囚禁，原子分子在强场下的偏移、加速和减速。通过对这些强场下原子分子动力学过程的解释，人们建立了全新的非微扰理论模型，不仅延伸了在传统微扰区弱光条件下形成的对光与物质相互作用的理解，还带来了许多重要的应用前景，包括产生相干X射线源和阿秒脉冲，分子轨道成像，超快电子衍射以及控制光化学反应。 然而，近来的实验发现，在强激光场作用下，分子不仅会发生电离形成分子离子，而且可以在分子离子的两个能级之间建立粒子数反转，从而诱导激光现象。进一步的研究发现这种强场电离诱导的激光行为在空气、N2、CO2等气体分子中都能实现，并且具有高亮度、线偏振、高度相干性等特点，不仅为非线性光谱学研究提供了全新的技术手段，和为强场分子动力学探测开辟了新途径，而且对其本身物理机制的探索将使得人们对强场电离理论、分子转动行为有更加全面、深入地认识。 基于上述背景，本论文对强场电离诱导的空气激光光谱学进行了细致研究，旨在以这种超快激光为手段，研究分子波包动力学，并为其产生机制提供更多的实验证据和理论线索。本论文主要工作以及创新成果如下： 1.利用双色场泵浦-探测方案，研究了N2+的B2Ʃu+态和X2Ʃg+态之间不同振动态跃迁形成的两条激光谱线（~391nm和~428nm）的强度随泵浦光椭圆偏振度的变化。研究表明~428nm的激光随椭圆偏振度增加逐渐降低，与强场电离理论相符，而~391nm的激光在泵浦光椭偏度为0.3时达到最强。通过与背向N2+荧光信号对比，表明~391nm激光对泵浦光椭圆偏振依赖的反常行为可能是由于N2+基态X2Ʃg+振动态布居数变化导致，因此，本实验结果暗示可以通过改变驱动光场椭圆偏振度来控制分子的振动激发和振动态布居。 2.在ω+2ω双色场驱动产生的高亮度空气激光光谱中观察到了超精细的分子转动结构，并通过这一单发测量的空气激光光谱得到了分子中转动态的布居。通过测量空气激光辐射强度随双色场延时的变化进一步证实了分子相干转动波包的形成。实验表明飞秒激光脉冲驱动的超快空气激光可以有效地探测发生在皮秒时间尺度的分子转动动力学过程，这为实时监控分子转动波包的演化提供了全新手段。 3.在实验上展示了利用一束高能量、线偏振、800nm激光脉冲可以直接在低压纯氮气中产生高亮度的窄带N2+分子激光信号，并利用互相关方法测量了对应不同振动态跃迁的中心波长为391nm 和428nm的N2+分子激光脉冲的时间波形，发现N2+分子激光的持续时间都在皮秒量级，远大于泵浦激光飞秒量级的持续时间。
英文摘要	Strong field physics is one of the most significant research frontiers of contemporary physics. Over the past couple of decades intense lasers with very high focusing intensities have become the main impetus in the researches of light-matter interactions, thanks to the state of the art ultrashort laser generation and chirped pulse amplification technologies. Atoms and molecules exposing to the intense laser pulses have exhibited many novel phenomena, including high-order harmonics generation, above-threshold ionization and dissociation, bond softening and hardening, Coulomb explosion, rotational excitation and molecular alignment, population trapping, plus deflection, acceleration and deacceleration of atoms and molecules. A new non-perturbative theoretical model has been established via the intensive investigations of these strong field atomic and molecular phenomena, which not only sheds more light on the physical processes underlying laser-matter interactions, but also brings about a variety of significant applications, such as generation of coherent X-ray sources and attosecond light pulses, molecular orbital imaging, ultrafast electron diffraction and robust control of photo-chemical reactions. However, it was discovered recently that molecules exposed to very short intense laser pulses not only become ionized but can also produce lasers. Apparently, an inversion in the population distribution of the molecular ions takes place: A higher-energy state becomes more populated than a lower-energy state. Such strong-field-induced population inversion has been seen in a number of molecular gases, including N2, CO2, and H2O, as well as air, and leads to lasing from the molecular gases. The mechanism behind this “air-lasing” phenomenon is sure to be fundamentally different from that underlying conventional lasers and is being actively investigated and hotly debated. Based on the above mentioned backgrounds, a systematic study on the strong-field-ionization induced air lasing phenomenon has been conducted in this thesis. The main achievements and innovative outcomes are listed as follows: 1.Investigating the dependence of the N2+ laser yields on the driving laser ellipticity using the two-color pump-probe experimental setup, and discovering that the ~391nm N2+ laser yield is maximized when an elliptically polarized laser is chosen as the pump source, while the ~428nm N2+ laser yield decreases monotonically as the ellipticity of the pump laser increases. These results also imply a new control knob on the vibrational excitation and vibrational states distribution of the molecular ions following strong-field-ionization. 2.Discovering the fine rotational spectral structure in the N2+ laser spectra driven by the two-color (ω+2ω) laser fields. Further demonstrating the modulation of N2+ laser yields stemming from the coherent rotational wave packets. These results exhibit that molecular rotation dynamics on picosecond timescale can be efficiently detected by ultrafast air laser driven by femtosecond laser pulses. 3.Demonstrating the N2+ laser can be induced in low pressure gaseous nitrogen by the intense infrared femtosecond laser pulse alone, plus the detailed measurements of the spatio-temporal shape of the N2+ laser by cross correlation measurements.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15887]
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	张海粟. 强场电离诱导产生空气激光光谱学研究[D]. 中国科学院上海光学精密机械研究所. 2014.

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