Development of an Ultraviolet Femtosecond Radiation Source -for Time-Resolved Excited-State Photoemission and - Flourescence Studies

该合同为千赫兹激光系统的开发提供部分支持，该系统旨在提供同步的近红外（~1.5eV）和紫外（~10eV）飞秒脉冲，适用于时间分辨、双光子、激发态角分辨光谱学（ARPES）。飞秒辐射源的发展将遵循啁啾脉冲放大和使用全固态钛蓝宝石激光技术的谐波产生方案的最新进展。该辐射源将与一台可用的ARPES光谱仪一起，通过利用红外脉冲光激发到费米能级以上未占据态的载流子动力学，初步用于确定高质量高tc超导体单晶的激发态电子结构。测定高tc铜酸盐的激发态电子结构将为我们理解这些材料中的超导机制提供独特的信息。这些测量将扩展到缠绕晶体和薄膜，以研究晶界和缺陷对高tc超导体电子结构和态密度的影响。这种超快双脉冲测量技术提供的本征时间分辨率将用于通过与单晶光激发载流子动力学的比较来确定缺陷和晶界对电子复合速率的影响。并计划进一步扩展该实验技术，以研究与技术相关的高tc超导线材料的电子特性。飞秒辐射源也将用于研究单生物分子动力学与非简并双光子共聚焦荧光显微镜。目的是确定使用该技术研究单个蛋白质分子构象波动的可行性，并通过高分辨率分子跟踪监测蛋白质诱导的DNA折叠动力学。分子构象波动的生物物理学知识是我们理解蛋白质和DNA折叠动力学的基础，因此也是酶的运作。此外，该飞秒激光脉冲源还计划在多个不同领域进行进一步的研究；高tc超导体的时间分辨太赫兹光谱，原叶绿素内酯氧化还原酶反应机理的测定，新型磁性多层材料的超快光谱，半导体异质结构中载流子动力学的相干控制，以及分子的时间分辨光解。%%%***

9803028SchroederThis award provides partial support for the development of a kilohertz laser system designed to provide the synchronized near infrared (~1.5eV) and ultraviolet (~10eV) femtosecond pulses suitable for time-resolved, two-photon, excited-state angle-resolved photoemission spectroscopy (ARPES). The development of the femtosecond radiation source will follow recent advances in chirped pulse amplification and harmonic generation schemes using all solid-state Ti:sapphire laser technology. Together with an available ARPES spectrometer, this radiation source will be used initially to determine the excited-state electronic structure of high-quality high-Tc superconductor single crystals by exploiting the dynamics of carriers photoexcited by the infrared pulse into the unoccupied states above the Fermi level. Determination of the excited state electronic structure of high-Tc cuprates should provide unique information relevant to our understanding of the superconducting mechanism in these materials. These measurements will be extended to twined crystals and thin films in order to study the effect of grain boundaries and defects on the electronic structure and density of states of high-Tc superconductors. The intrinsic temporal resolution provided by this ultrafast two-pulse measurement technique will be used to determine the effect of defects and grain boundaries on electron recombination rates through a comparison with the photoexcited carrier dynamics in single crystals. The further extension of this experimental technique to study the electronic properties of technologically relevant high-Tc superconducting wire materials is also planned.The femtosecond radiation source will also be used to investigate the dynamics of single biological molecules with non-degenerate two-photon confocal fluorescence microscopy. The intent is to determine the feasibility of using this technique to study conformational fluctuations of single protein molecules and to monitor protein-induced DNA folding dynamics through high-resolution molecular tracking. Knowledge of the biophysics of molecular conformational fluctuations are fundamental to our understanding of protein and DNA folding dynamics, and hence, also the operation of enzymes.In addition, future research is planned with this source of femtosecond laser pulses in several diverse fields; time-resolved THz spectroscopy of high-Tc superconductors, determination of the reaction mechanism of protochlorophyllide oxidoreductase, ultrafast spectroscopy of novel magnetic multilayer materials, coherent control of carrier dynamics in semiconductor heterostructures, and the time-resolved photodissociation of molecules.%%%***