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.

在这个项目中，将探索将非线性光学扩展到光谱的软X射线区域的新技术。具体地说，精确控制的光学波形、结构波导和短波长的准相位匹配将被用来增加基于激光的相干X射线源的亮度。在过去的两年里。这一ARCA取得了巨大的进展，展示了将波长约为50 eV的激光有效地转换到光谱的极端紫外线(EUV)区域的新方法。现在可以产生比同步加速器产生的短1000倍的短波长光脉冲--足够短(10飞秒)来直接探测原子运动。通过使用相位匹配技术，还可以显著提高这些非常高阶的非线性过程的转换效率。例如，通过通过中空光纤传输激光，可以使光脉冲的相速度与产生的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，使优化过程和选择性地增强特定的X射线光子能量成为可能。这是一种发生在单个原子内的根本新型的相位匹配，其中激光脉冲形状经过优化，使得激光的一个半周期产生的X射线与相邻半周期产生的X射线建设性地干扰。这与更传统的相位匹配技术形成了鲜明的对比，在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建设性干涉。在拟议的工作中，将解决在EUV中产生相干光的几个重要挑战。新的技术将被开发出来，它将允许我们将相位匹配技术应用于更高的光子能量，从50-500 eV。简单地扩展之前的工作是不够的，因为更高能量的X射线光子是在更高水平的电离下发射的，在激光和X射线光束之间引入了非常大的相速度失配。可能的新技术包括使用结构波导来调制系统的非线性响应以获得准相位匹配，以及使用双色激发。这项工作与使用时间形状脉冲的持续工作相结合，将极大地提高对这一高度非线性区域中激光-原子相互作用的理解，以及我们优化控制X射线产生过程的能力。这一研究领域是前沿基础研究和先进技术的独特和具有挑战性的结合。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，其非常实用的目标是开发明亮、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。这项工作将为学生在光学、计算机、电子和EUV技术方面提供出色的培训，这些领域具有重要的技术意义，在这些领域，行业的需求远远超过毕业生的可获得性。此外，这种新光源在纳米技术、显微镜、计量学、光刻、X射线光学表征以及利用X射线研究超快动态过程中具有潜在的应用前景。我们和其他公司正在积极寻求其中的许多应用。