Atomistic dynamics of photoinduced effects in chalcogenide glass

1. Laser, cw/pulsed X18B-X19A Atomistic dynamics of photoinduced effects in chalcogenide glass Donghui Zhao and Himanshu Jain Department of Materials Science and Engineering, Lehigh University, PA 18015 • Chalcogenide glasses (ChG) are made of Group VI element(s) (S, Se, and Te), often alloyed with Group IV and/or V elements (e.g. As, Sb, Ge etc). They exhibit many unusual, but very useful photoinduced effects. For example, band gap light can change their optical absorption, refractive index, chemical reactivity, and volume. As a result, integrated optical devices, such as waveguides, resonators, and photonic crystals, can be fabricated by direct laser writing and photolithography on the thin films of ChG. • In situ X-ray absorption spectroscopy (XAS) is critical for the fundamental understanding of atomistic mechanisms of photosensitivity of these materials. It is found that a photochemical reaction is triggered locally in which the non-equilibrium homopolar bonds (e.g. As-As, S-S) are converted into heteropolar bonds (e.g. As-S). This bond switching process drives the expansion of bond length throughout the network structure of the material. • The state-of-the-art time-resolved XAS provides the first-hand information about the atomistic dynamics of photostructural changes in ChG. It is found that the bonds expand as an exponential function of laser exposure time. Objective lens Direct laser writing!! Photolithography Fresnel lens 100 μm A Kovalskiy et al., 2009 • Laser-induced material modification • Refractive index: n’>n0 • Photodarkening: α’>α0 • Chemical reactivity • Volume change K Tanaka et al., 2006 Bond switching Atomistic dynamics: bond expansion n’ Waveguide Photoexpansion n0 Moving stage Chalcogenide glass thin film Quartz glass substrate Work performed on beamlines X18B and X19A.