Microstructures induced by femtosecond laser pulses inside glasses
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Jianrong Qiu State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
John C.H. Spence Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (Received 21 July 2008; accepted 1 December 2008)
In this article, the chemical and structural changes inside soda-lime glasses induced by femtosecond (fs) laser pulsing have been reported, based on transmission electron microscopy and electron energy loss spectroscopy studies. Under fs-laser interaction, Na-rich phases are formed, and Na nanoparticles are also precipitated around the Na-rich phases. These findings demonstrate how powerful and efficient the fs-laser pulsing and interaction can be in making novel microstructures in soda-lime silicate glass, and they bridge the gap between the macroscale property changes and nanometer-scale structures. I. INTRODUCTION
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 sub-band gap wave length 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.1–11 It is generally believed that fs-laserinduced 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 understanding how transparent materials respond to fslaser irradiation. Various scenarios have been proposed to evaluate the individual data of spectroscopy, fluorescence, ESR, and other methods.12–14 A possible reason for the confusion over mechanisms is that the laser-induced changes depend on various parameters, including laser power, duration of time, focusing, and materials, and thus several mechanisms are likely to play different roles depending on experimental conditions.15 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. In this study, we report for the first time the microstructural changes and a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0225 J. Mater. Res., Vol. 24, No. 6, Jun 2009
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local composition in fs-laser irradiated soda-lime silicate glass using transmission electron microscopy (TEM) combined with the time-dependent electron energy-loss spectroscopy (EELS) technique. We found that in the fslaser irradiated area, the glass separates into Na-rich and poor phases and Na nanoparticles are also precipitated around the Na-rich phases. Our results demonstrate how po
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