基于中红外飞秒激光场的超快非线性光学若干问题的研究
文献类型：学位论文
| 作者 | 储蔚 |
| 学位类别 | 博士 |
| 答辩日期 | 2012 |
| 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 | 飞秒激光，中红外，超快光学，高次谐波（HHG），阈上电离（ATI），成丝， 远程空气激光。 |
| 其他题名 | Investigations on Ultrafast Nonlinear Optics Based on Mid-infrared Femtosecond Laser Sources |
| 中文摘要 | 随着超快激光技术的发展以及可调谐中红外新波段激光光源的出现，强激光场中原子和分子物理学的研究也步入了新的空间。高次谐波产生在合成阿秒脉冲以及得到高能高亮的光子方面有着重要的意义。基于中红外激光场的高次谐波辐射在产生更高能量的光子、合成更短的阿秒脉冲等方面具有巨大的优势，而中红外飞秒激光成丝诱导的远程空气激光在大气探测等方面也有着重要的潜在应用。 本论文利用中红外飞秒激光场，一方面研究了原子内库伦势对高能区电子波包动力学的影响，另一方面，发现了在中红外激光成丝过程中产生的基于种子效应的远程空气激光和二氧化碳(CO2)气体中的受激放大光辐射。此外，利用双色场聚焦在空气中，发现了成丝过程中的三倍频双通道干涉效应。主要工作和创新性成果如下： 1. 通过理论和实验相结合的方法验证了在高能区强场近似模型的失效，通过将库伦势引入半经典计算，我们揭示了原子中库伦势对高能区返回电子的作用机制。 2. 首次利用中红外可调谐激光脉冲在成丝过程中实现了高亮度、波长可切换的远程空气激光。由于是由强场直接电离氮离子内壳层价电子形成粒子数反转，所以该过程发生在超快时间范畴。与以往的研究不同，该空气激光辐射对泵浦波长极其敏感，通过调节中红外激光的波长，不仅可以有效地控制空气激光的强度，而且成功地实现了远程空气激光波长的转换。 3. 通过中红外激光场在CO2中成丝，产生了远程激光辐射。基于CO2的远程激光辐射谱具有明显的双峰结构，并且同时激发多条谱线。这种受激辐射的相干性被双缝干涉的图案所证明。本实验结果在有效探测CO2气体含量，控制温室效应等方面有一定的意义。 4. 研究了双色场中的三次谐波行为。首次观测到在800 nm和其二倍频400 nm所形成的双色场成丝过程中的三倍频双通道干涉现象： 三倍频强度以0.67 fs为周期进行调制。实验发现在不同的泵浦激光功率下，这种三倍频的干涉呈现出不同的效应。该发现在泵浦光焦点处脉冲诊断方面有着潜在的应用。 |
| 英文摘要 | Strong field atomic and molecular physics has entered a new stage with the development of ultrafast laser technology and tunable infrared laser sources. High-order harmonic generation (HHG) driven by strong laser field provides a potential way for generating high energy, high-brightness extreme ultraviolet (XUV) sources and single attosecond (as) pulses. Recently, femtosecond pulses of longer driving wavelengths are increasingly used in ultrafast optics and strong field physics research, such as HHG, photoionization and filamentation. In fact, HHG driven by mid-infrared femtosecond laser have led to more efficient generation of high-energy XUV or soft X-ray photons deeply into the “water window” spectral region. Moreover, investigations on filamentation induced by mid-infrared femtosecond laser pulses have promoted potential applications in remote atmospheric sensing. In this Ph.D. dissertation, we experimentally investigate the influence of Coulomb potential on electron wavepacket dynamics in the high energy recollision region in ATI and HHG. processes. And we experimentally study harmonic seeded remote lasers in air and CO2. The main works and achievements are as follows: 1. The breakdown of Simpleman’s model for strong-field photoionization in the high energy recollision region has been revealed by combining theoretical and experimental methods. With the help of a semiclassical model calculation taking into account the Coulomb potential, we show that for the first time to our knowledge, for the high-energy recollision electrons, their wavepacket dynamics can still be strongly influenced by the Coulomb field. 2. The harmonic-seeded switchable multi-wavelength laser in air driven by intense mid-infrared femtosecond laser pulses has been experimentally demonstrated. Population inversion occurs at an ultrafast time-scale (i.e., less than ~200 fs) owing to direct formation of excited molecular nitrogen ions by strong-field ionization of inner-valence electrons. It is also found that the multi-wavelength remote laser is very sensitive to the pump wavelength. One can control the wavelength and intensity of the remote air laser by adjusting the wavelength of the infrared pump laser. This work opens the perspective for remote detection of multiple pollutants based on nonlinear optical spectroscopy. 3. We demonstrate multi-wavelength amplified harmonic emissions in carbon dioxide gas using intense mid-infrared femtosecond laser pulses. All these narrow-bandwidth emissions have a typical CO2+ two-peak structure. The coherence property of the amplified harmonic emissions is further evidenced by its diffraction pattern. This technique may be used for remote monitoring the CO2 flux in some plants to help control the greenhouse gas release to the atmosphere. 4. We experimentally demonstrate third harmonic generation (THG) by intense femtosecond laser pulse at a central wavelength of ~800 nm superposed by its second harmonic in air. The third harmonic signal shows a periodic modulation with a period of ~0.67 fs. The periodic modulation of THG has different effects under different experimental conditions. This work is expected to be a effective method for diagnosing on-focus laser pulse in the high-field laser physics. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15686]  |
| 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 | 储蔚. 基于中红外飞秒激光场的超快非线性光学若干问题的研究[D]. 中国科学院上海光学精密机械研究所. 2012. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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