MRI: Acquisition of a High Intensity Tunable Femtosecond Laser.

该NSF-MRI允许在中红外（1400-2200 nm）光谱区域中产生载波包络相位稳定的毫焦耳（mJ）级、少周期脉冲（10 fs至14 fs）。为了产生这些脉冲，白光种子光参量放大器（OPA）是由20 mJ飞秒激光泵浦。然后，从OPA出现的脉冲被光谱展宽和压缩。这种能力处于当前超快物理学和阿秒科学的最前沿，为激光-物质相互作用的一般领域的新的和令人兴奋的研究打开了一扇窗户。将这些脉冲扩展到中红外应该会增强高次谐波的产生-目前世界各地只有少数实验室在努力。用这些较长的波长驱动谐波将导致更高的光子通量和能量。这种高的光子通量是至关重要的非线性UV/XUV现象的研究，以及扩展我们的研究，以更复杂的系统的利益，为大多数应用程序。 更长波长的驱动激光器也将使电子动力学的研究使用一个非常不同的，而非正统的方法。 也就是说，通过利用某些分子中的解离几乎是原子中电离的完美模拟这一事实，只需要很少的飞秒激光脉冲，因为原子核的移动速度比电子慢得多。 然而，这些脉冲必须具有长波长才能产生可测量的信号。 除了科学进步之外，还将追求技术进步，例如对阿秒脉冲进行整形以消除其自然啁啾或对其进行调整以驱动特定的动态。 这种能力将是一个重大的成就，并将反过来，使进一步的科学进步，因为科学和技术的突破在这一领域齐头并进。测量和控制物质中的电子的动力学是贯穿大部分原子，分子和光学（AMO）物理，化学，材料科学，甚至今天的生物学的主要主题。事实上，正如能源部2007年BESAC特别报告中所确定的，五个“基础能源科学的重大挑战”中的第一个是“我们如何在电子水平上控制材料过程？这个主题再次出现在国家研究理事会的“物理学2010”报告中，AMO的贡献题为“控制量子世界”。“为了实现这些目标，需要几十阿秒（1 as = 10^-18 s）量级的激光脉冲。这种脉冲的产生是一个挑战，但是通过使用高次谐波产生（HHG），世界上一些领先的实验室已经获得了低于100的脉冲，包括在J. R。麦克唐纳实验室（JRML）。这一技术突破催生了阿秒科学领域，这是目前AMO物理中最热门的领域之一。该项目将利用这些阿秒紫外/极紫外脉冲来研究原子和分子动力学以及探测更复杂的凝聚态系统。此外，通过观察HHG光谱和/或发射的电子，可以观察到分子的结构变化，加深我们对潜在动力学的理解，从而在量子力学水平上控制化学反应方面迈出重要一步。除了技术和科学影响外，该基金还通过对大约7名博士后的实践培训，对大量年轻科学家产生了重大影响，16名研究生和5名本科生由JRML主办。虽然培训机会主要使研究生和博士后研究员受益，但它们也对本科生产生影响，例如，物理系的本科生研究经验（REU）计划由NSF资助。然而，这种激光源也在来自三个EPSCoR州的机构的参与者之间建立了非常广泛的合作，这些机构目前主要由NSF和DOE资助。参与的机构有堪萨斯州立大学、路易斯安那州立大学、奥古斯塔纳学院（南达科他州的一所本科院校）和堪萨斯大学。JRML集团将利用这一新的激光系统，按照这一模式开展更多的合作。

This NSF-MRI allows generating milli-Joule (mJ) level, few-cycle pulses (10 fs to 14 fs) in the mid-infrared (1400-2200 nm) spectral region that are carrier-envelope phase stable. To generate these pulses, a white-light seeded optical parametric amplifier (OPA) is pumped by a 20 mJ femtosecond laser. The pulses emerging from the OPA are then spectrally broadened and compressed. Such capabilities are at the forefront of current ultrafast physics and attosecond science, opening a window for new and exciting studies in the general area of laser-matter interaction.Extending these pulses to the mid-IR should enhance high-harmonic generation -- an effort presently pursued at just a handful of laboratories around the world. Driving the harmonics with these longer wavelengths will lead to a higher photon flux and energy. This high photon flux is critical for studies of non-linear UV/XUV phenomena as well as for extending our studies to the more complex systems of interest for most applications. The longer wavelength driving laser will also enable the investigation of electronic dynamics using a very different, rather unorthodox, approach. Namely, by taking advantage of the fact that dissociation in some molecules is an almost perfect analog of ionization in atoms, only few femtosecond laser pulses are required since nuclei move much slower than electrons. These pulses must, however, have long wavelengths to produce a measurable signal. In addition to the science advances, technological advances such as shaping attosecond pulses to eliminate their natural chirp or tailoring them to drive specific dynamics will be pursued. Such capabilities would be a substantial accomplishment and would, in turn, enable further scientific advances since scientific and technological breakthroughs go hand-in-hand in this field.Measuring the dynamics of and controlling electrons in matter are major themes that extend throughout much of atomic, molecular and optical (AMO) physics, chemistry, materials science, and even biology today. In fact, the first of the five "Grand Challenges for Basic Energy Science," as identified in the Department of Energy's special BESAC report in 2007, is "How do we control material processes at the level of electrons?" This theme appeared again in the National Research Council's "Physics 2010" report where the AMO contribution was entitled "Controlling the Quantum World." To accomplish these goals, laser pulses on the order of tens of attoseconds (1 as = 10^-18 s) are required. Such pulses are a challenge to produce, but by using high-harmonic generation (HHG), pulses below 100 as have been obtained in a few leading labs around the world, including here at the J. R. Macdonald Laboratory (JRML). This technological breakthrough has given birth to the field of attosecond science, which is presently one of the hottest in AMO physics. This project will employ these attosecond UV/XUV pulses to study atomic and molecular dynamics as well as to probe more complex condensed matter systems. In addition, by observing the HHG spectra and/or emitted electrons, structural changes in molecules can be observed as they happen, deepening our understanding of the underlying dynamics and thereby taking an important step in controlling chemical reactions at the quantum mechanical level.Beyond the technical and scientific impacts, this grant significantly impacts a large number of young scientists through hands-on training of the roughly seven postdocs, sixteen graduate students, and five undergraduate students hosted by the JRML. While the training opportunities mainly benefit graduate students and postdoctoral fellows, they also have an impact on undergraduate students through, for instance, the Physics Department's Research Experiences for Undergraduates (REU) program funded by the NSF. However, this laser source has also created a very broad collaboration between participants from institutions in three EPSCoR states who are currently funded primarily by NSF and DOE. The institutions involved are Kansas State University, Louisiana State University, Augustana College (an undergraduate institution in South Dakota), and the University of Kansas. The JRML group will leverage this new laser system to initiate additional collaborations following this model.