Dynamics of Localized Photoexcitations in Condensed Matter Systems Susan L. Dexheimer, Washington State University, DMR Localization of electronic excitations is a phenomenon that has a dramatic impact on optical and electronic properties of materials and reflects fundamental interactions in the physics of condensed matter systems. We are using femtosecond laser spectroscopic techniques that are sensitive to both electronic and vibrational dynamics to study the physics of the formation and evolution of localized electronic excitations. Our studies are carried out in materials in which the key physical interactions, the electron-electron and electron- phonon interactions, can be systematically tuned. Carrier localization dynamics associated with coupling of electronic excitations to optical and acoustic phonon modes are observed using femtosecond vibrationally impulsive excitation techniques, in which optical pulses short compared to the characteristic vibrational periods are used to time- resolve atomic-scale vibrational motions. Studies of polaron formation and evolution are made possible using recently developed time-resolved measurement techniques in the THz, or far-infrared, spectral range. In quasi-one-dimensional materials, we find that the dynamics of exciton-polaron formation, in which an initially delocalized electronic state localizes through its interaction with the lattice, occur on the time scale of a single vibrational period, essentially as fast as is physically possible for a structural transformation to take place. [Pt(en) 2 ] [Pt(en) 2 X 2 ]. ClO 4 X = Cl, Br, I en = ethylenediamine (C 2 H 8 N 2 ) Structurally tunable quasi-one-dimensional mixed-valence linear chain complexes

Broader impact Molecular-based and nanoscale electronic materials have significant potential for the development of new technologies for a wide range of applications. This work contributes to the understanding of key fundamental physical processes that are important for future technological development. Education and outreach activities Two undergraduate students, three graduate students, and one postdoctoral associate have gained research training while working on research supported by this NSF award. The PI teaches classes at the undergraduate and graduate levels in optical physics, solid state and materials physics, optoelectronics, and quantum electronics, and makes use of research activities and results in classroom instruction. The PI currently serves as director of a scholarship program focused on recruiting and retaining women physics students at WSU. A number of high school student groups from throughout the state of Washington have toured our laser laboratories as part of the outreach activities of the WSU Department of Physics and Astronomy. Dynamics of Localized Photoexcitations in Condensed Matter Systems Susan L. Dexheimer, Washington State University, DMR Graduate student Fran Morrisey and undergraduate physics majors Erin Craig and Keith Myers optimize a femtosecond regenerative amplifier