Enhanced Functionality for Materials Analysis in the DTEM

We propose time-resolved and static energy-loss spectroscopy with nanometer spatial resolution both to understand damage processes by high powered lasers in optical elements, and also as a means of lithographic nanostructural fabrication in photonic glasses. The research will use facilities at ASU (new aberration-corrected STEM with EELS), NCEM LBNL (LIbra monochromated STEM) and at LLNL (DTEM). In 2007, a workshop sponsored by NSFs International Materials Institute (IMI) for New Functionality in Glass recommended that micro/nanopatterning and lithography in transparent materials was the most deserving research topic for introducing new functionalities of glass in electronic applications and nanostructures. Since the discovery of ultrashort pulsed laserinduced refractive-index-changed microstructures in silicate glasses in the mid 1990s, the use of high-power ultrashort pulse lasers for modifying glasses has opened new frontiers in the physics and technology of light-mater interactions [1, 2]. Structural and chemical modification is a fascinating phenomenon of high-power femtosecond (fs) laser pulsing and interactions in transparent materials. The interaction is confined to within such a short period that thermal diffusion can be ignored in some materials, such as silicate glasses. Therefore, focused subbandgap wavelength fs-laser pulses can efficiently and precisely deposit energy into a micrometer-sized focal volume and thus induce localized structural and chemical changes inside the bulk [3]. It is generally believed that fs-laser-induced change is initiated by an avalanche ionization process with different contributions of multiphoton and/or tunneling excitation of electrons, and therefore exhibits a highly nonlinear dependence on the intensity of the illuminating laser beam. However, current experimental research does not provide a sufficient basis for an understanding how transparent materials respond to fs-laser irradiation. Various scenarios have been proposed to evaluate the individual data of spectroscopy, fluorescence, ESR, and other methods [4 6]. A possible reason for confusion over mechanisms is that the laser-induced changes depend on various parameters, including laser power, pulse, focusing and materials, and thus several mechanisms are likely to play different roles depending on experimental conditions [7]. The lack of any direct observation and determination of the exact phase state and distribution in space of laser-irradiated glasses also contribute to uncertainty. Therefore, we propose a thorough research program on the detailed microstructural changes inside transparent materials induced by fs laser pulses. The work will also expose the mechanisms of damage by high powered lasers on optical elements , such as those used in laser fusion experiments. This program is built on the several years experience in the study of glass microstructures and modifications by the principle investigator (NJ) at ASU. In particular, we have been funded by the NSF in the study of direct-write electron lithography in glasses (NSF DMR0245702 and DMR0603993), and have developed a time-resolved parrallel-detection energy-loss spectrsocopy method with nanometer spatial resolution for this purpose. IN parallel with the DTEM time-resolved imaging work at LLNL, we plan to continue this time-resolved energy-loss spectroscopy work on the early stages of bond-breaking in silicates, in order to understand the mechanisms of lithography and radiation damage. We have more than 40 publications during the last 6 years in refereed international journals on the relevant topics. . The expertise within ASU will focus on microstructure study using the facilities within the LeRoy Eyring Center for Solid State Science and John Cowley Center for High Resolution Electron Microscopy. The in situ work of transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) will be done on the