Quantum Control of Coherent EUV Radiation: New Methods for Phase Matching at Short Wavelengths

相干 EUV 辐射的量子控制：短波长相位匹配的新方法

• 批准号: 0099886
• 负责人: Margaret Murnane
• 金额: $ 30万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-07-01 至 2004-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0099886&HistoricalAwards=false
• 关键词: Quantum; Control; Coherent; EUV; Radiation

In this project, new techniqucs to extend nonlinear optics into the soft-x-ray region of the spectrum will be explored. Specifically, precisely controlled optical waveforms, structured wave guides, and quasi phase-matching at short wavelengths will be used to increase the brightness of laser-based coherent x-ray sources. In the past 2 years. dramatic progress has been made in this arca, demonstrating new methods for efficient conversion of laser light into the extreme ultraviolet (EUV) region of the spectrum, at wavelengths around 50eV. It is now possible to generate short- wavelength light pulses 1000 times shorter than can be generated by synchrotrons-short enough (10 femtoseconds) to directly probe atomic motion. It is also possible to dramatically improve the conversion efficiency of these very high-order nonlinear processes by using phase matching techniques. For example, by propagating the laser beam through a hollow fiber, the phase velocity of the optical pulse can be made to match that of the generated x-ray beam, thus improving thc conversion efficiency. Finally, very recently it was shown that feedback-control algorithms can fine- tune the shape in time of the laser pulse driving high-harmonic generation, making it possible to optimize the process and selectively enhance a particular x-ray photon energy. This is a fundamentally new type of phase matching that occurs within a single atom, where the laser pulse shape is optimized so that x-rays generated from one half-cycle of the laser interfere constructively with x-rays generated by adjacent half-cycles. This is in contrast to more-conventional phase matching techniques, where emission from a large number of individual atoms is arranged to interfere constructively by matching the phase velocities of the driving and harmonic waves.In the proposed work, several significant remaining challenges for generating coherent light in the EUV will be addressed. New techniques will he developed that will allow us to apply phase- matching techniques to higher photon energies, from 50 - 500eV. Simply extending previous work will not suffice because higher-energy x-ray photons are emitted at higher levels of ionization, introducing a very large phase velocity mismatch between the laser and x-ray beams. Possible new techniques include the use of structured waveguides for modulating the nonlinear response of the system to obtain quasi phase matching, and the use of two-color excitation. This work, when combined with continuing work on the use of temporally-shaped pulses, will greatly enhance the understanding of laser-atom interactions in this highly nonlinear-regime, and our ability to optimally control the x-ray generation process.This area of research presents a unique and challenging combination of forefront basic research and advanced technology. Ultrafast, broad bandwidth laser pulses and feedback algorithms will be used to coherently control and engineer the electron wave function of a radiating atom, with the very practical objective of developing bright, coherent, soft-x-ray light sources. This control of matter on the sub-nanometer, sub-femtosecond, distance- and time-scales explores the limits of fundamental atomic and molecular processes, as well as of optical technology. This work will provide excellent training for students in optical, computer, electronic, and EUV technologies- technologically- significant fields where the needs of industry far outpaee the availability of graduates. Furthermore, this new light-source has potential future applications in nanotechnology, microscopy, metrology, lithography, the characterization of x-ray optics, and in the study of ultrafast dynamic processes using x-rays. We and other are actively pursuing many of these applications.

在该项目中，将探索将非线性光学扩展到软 X 射线光谱区域的新技术。具体来说，精确控制的光学波形、结构化波导和短波长的准相位匹配将用于提高基于激光的相干 X 射线源的亮度。在过去的2年里。这一领域取得了巨大进展，展示了将激光有效转换到波长约为 50eV 的极紫外 (EUV) 光谱区域的新方法。现在可以产生比同步加速器产生的短波长光脉冲短1000倍的光脉冲——足够短（10飞秒）以直接探测原子运动。通过使用相位匹配技术，还可以显着提高这些非常高阶非线性过程的转换效率。例如，通过中空光纤传播激光束，可以使光脉冲的相速度与生成的X射线束的相速度相匹配，从而提高转换效率。最后，最近的研究表明，反馈控制算法可以及时微调驱动高次谐波产生的激光脉冲的形状，从而可以优化过程并选择性地增强特定的 X 射线光子能量。这是一种发生在单个原子内的全新类型的相位匹配，其中激光脉冲形状经过优化，使得激光半周期产生的 X 射线与相邻半周期产生的 X 射线相长干涉。这与更传统的相位匹配技术形成鲜明对比，在更传统的相位匹配技术中，大量单个原子的发射被安排为通过匹配驱动波和谐波的相速度来进行相长干涉。在所提出的工作中，产生相干波的几个重大挑战EUV 中的光将得到解决。他将开发新技术，使我们能够将相位匹配技术应用于更高的光子能量，从 50 - 500eV。简单地扩展以前的工作是不够的，因为更高能量的 X 射线光子在更高的电离水平下发射，从而在激光和 X 射线束之间引入非常大的相速度不匹配。可能的新技术包括使用结构化波导来调制系统的非线性响应以获得准相位匹配，以及使用双色激励。这项工作与使用时间形状脉冲的持续工作相结合，将极大地增强对这种高度非线性机制中激光-原子相互作用的理解，以及我们优化控制 X 射线生成过程的能力。研究呈现了前沿基础研究和先进技术的独特且富有挑战性的结合。超快、宽带激光脉冲和反馈算法将用于相干控制和设计辐射原子的电子波函数，其非常实际的目标是开发明亮、相干的软 X 射线光源。这种在亚纳米、亚飞秒、距离和时间尺度上对物质的控制探索了基本原子和分子过程以及光学技术的极限。这项工作将为光学、计算机、电子和 EUV 技术等技术重要领域的学生提供出色的培训，这些领域的行业需求远远超出了毕业生的供应。此外，这种新光源在纳米技术、显微镜、计量学、光刻、X射线光学表征以及使用X射线的超快动态过程研究中具有潜在的未来应用。我们和其他人正在积极寻求其中的许多应用。