Itzhak Ben-Itzhak - US grants

In this award, Professors Itzhak Ben-Itzhak and Charles L. Cocke of Kansas State University, together with their graduate and undergraduate student researchers, will collaborate with the group of Matthias F. Kling of the Max-Planck Institute of Quantum Optics (Garching, Germany), in a study of the dynamics of molecular dications produced with attosecond light pulses. Specific systems to be studied include acetylene dication and nitric oxide dication. In the case of acetylene, they will search for evidence of acetylene-vinylidene isomerization. The experiments combine the COLTRIMS technique developed at Kansas State with advanced extreme ultraviolet/attosecond pulse generation methods developed at the MPQ. This international collaborative research project is supported jointly by the Experimental Physical Chemistry Program of the Chemistry Division and the Office of International Science and Engineering of NSF as well as by the Deutsche Forschungsgemeinschaft (DFG).

Electrons are the glue which bind the atomic constituents of molecules together. Their motion is on the attosecond timescale. Scientists like Ben-Itzhak, Cocke and Kling are using attosecond light pulses as a stroboscopic means of taking snapshots of the electron dynamics in molecules. The ultimate aim of research like this is to develop a nuanced picture of the ways in which chemical reactions take place. Besides the broad scientific impact of this work, the student researchers from Kansas State University working on this project will conduct a significant portion of their work at a premier laboratory in Germany -- thus helping to develop the next generation of globally-engaged young scientists.

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.

Non-technical Description
The atomic, molecular, and optical (AMO) research groups in Nebraska and Kansas will form a collaborative consortium to study and develop ways to control fundamental processes of electron motion in atoms, molecules, and nanostructures that occur at ultrafast (femto (10-15) to atto (10-18) second) time scales. The project will bring together experimental and theoretical physicists, chemists and electrical engineers from the University of Nebraska at Lincoln (UNL), the Kansas State University (KSU), and the University of Kansas (KU) as well as the facilities for AMO research at the James R. Macdonald Laboratory (JRML) at KSU, Extreme Light Laboratory at UNL, Physics and Chemistry departments at KU, and the computing resources at the partner institutions to explore novel states of matter. The project team plans to engage in synergistic activities to expand and diversify the STEM workforce by engaging students, teachers, and researchers at broad ranging educational levels. Research and educational collaborations among the consortium partners as well as at national and international levels and the preparation of a diverse, globally engaged STEM workforce training are expected to be sustained beyond the award period.
Technical Description
The projects will use femto to atto second pulses of light to trigger different types of reactions in matter and use pump-probe measurements, high harmonic generation, and ultrafast electron diffraction methods to study and image atomic and molecular motions. Detailed experimental and theoretical studies will be carried out to understand the molecular ionization processes caused by the interaction of strong laser fields and molecules. Participating researchers will build an electron spectrometer with angular resolution, improve the accuracy of extracting the molecular structure parameters, and establish an improved ionization theory for polyatomic molecules. Another aspect of the project will focus on experimental and theoretical studies to investigate the interaction of nanostructures to ultrashort pulses of extreme ultraviolet and infrared radiation. Applications such as ultrafast optical free electron beam switches will also be explored. The project will leverage the infrastructure and education, diversity, and outreach programs established by Kansas and Nebraska Experimental Program to Stimulate Competitive Research (EPSCoR) to engage and inspire students at all levels. During the three years of this Research Infrastructure Improvement Track-2 project, the program expects to provide 19 person-years of postdoctoral training and support 48 graduate students, 18 undergraduates and 18 faculty members from two-and four-year colleges, 18 high school students, and 30 high school teachers in research.

The ability to predict and control the outcome of chemical reactions is essential for many areas of modern physics, chemistry and biology. This ability requires detailed knowledge of how individual atoms in molecules move to break, form, or rearrange chemical bonds between them during the reaction. This research project aims at obtaining high-resolution movies of such atomic motion. Since the atoms involved in chemical reactions move extremely fast, typically on a time scale of few tens of femtoseconds (one femtosecond is one millionth of a billionth of a second), ultrashort, femtosecond laser pulses are the only experimental tools capable of recording such movies in real time. However, because of the quantum nature of atoms and molecules, the outcome of any molecular reaction is not deterministic: even if one measurement precisely captures the positions of all atoms at a given time, the same measurement will have different outcomes if repeated several times, even under exactly identical conditions. The acquisition of a high-power laser system delivering a hundred thousand pulses (each shorter than 10 femtoseconds) per second will enable repeating such measurements millions of times, which is needed for the creation of a quantum-mechanical molecular movie. Each frame of a movie then reflects the probability of every possible configuration of atoms at different stages of the reaction, instead of a fixed picture of a molecule. Such movies will advance our understanding of fundamental chemical processes and provide input for applications in areas of national priority, ranging from efficient energy conversion and storage to synthesis of novel materials, drug design and molecular electronics. This project is jointly funded by the Major Research Instrumentation program and the Established Program to Stimulate Competitive Research (EPSCoR).


Within this project, a broad range of photochemical processes, including photodissociation and isomerization, charge transfer reactions and formation of van der Waals clusters, will be studied. For each of these processes, the main scientific goal is to image the time-dependent molecular geometry and simultaneously characterize the evolving electronic structure of the molecule. This will be achieved by employing several complementary time-resolved techniques, including photoelectron spectroscopy and ion momentum imaging, inner-shell and laser-induced photoelectron diffraction, as well as ion beam techniques and Fourier-transform spectroscopy for characterization of the neutral fragments. For all these techniques, the key technical aspect facilitating simultaneous characterization of electronic and nuclear degrees of freedom will be the coincident detection of several reaction products, enabled by the high repetition rate of the acquired laser. At the same time, its high average power of several hundred watts will enable the efficient conversion of the emitted near-infrared radiation to a broad range of different wavelengths (from long-wavelength infrared to extreme ultraviolet and soft x-rays) needed for initiating and probing the reactions to be studied.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.