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.
